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diff --git a/docs/interop/bitmaps.rst b/docs/interop/bitmaps.rst index 7bcfe7f461..510e8809a9 100644 --- a/docs/interop/bitmaps.rst +++ b/docs/interop/bitmaps.rst @@ -1,5 +1,5 @@ .. - Copyright 2015 John Snow <jsnow@redhat.com> and Red Hat, Inc. + Copyright 2019 John Snow <jsnow@redhat.com> and Red Hat, Inc. All rights reserved. This file is licensed via The FreeBSD Documentation License, the full @@ -9,547 +9,1476 @@ Dirty Bitmaps and Incremental Backup ==================================== -- Dirty Bitmaps are objects that track which data needs to be backed up - for the next incremental backup. +Dirty Bitmaps are in-memory objects that track writes to block devices. They +can be used in conjunction with various block job operations to perform +incremental or differential backup regimens. -- Dirty bitmaps can be created at any time and attached to any node - (not just complete drives). +This document explains the conceptual mechanisms, as well as up-to-date, +complete and comprehensive documentation on the API to manipulate them. +(Hopefully, the "why", "what", and "how".) + +The intended audience for this document is developers who are adding QEMU +backup features to management applications, or power users who run and +administer QEMU directly via QMP. .. contents:: +Overview +-------- + +Bitmaps are bit vectors where each '1' bit in the vector indicates a modified +("dirty") segment of the corresponding block device. The size of the segment +that is tracked is the granularity of the bitmap. If the granularity of a +bitmap is 64K, each '1' bit means that a 64K region as a whole may have +changed in some way, possibly by as little as one byte. + +Smaller granularities mean more accurate tracking of modified disk data, but +requires more computational overhead and larger bitmap sizes. Larger +granularities mean smaller bitmap sizes, but less targeted backups. + +The size of a bitmap (in bytes) can be computed as such: + ``size`` = ceil(ceil(``image_size`` / ``granularity``) / 8) + +e.g. the size of a 64KiB granularity bitmap on a 2TiB image is: + ``size`` = ((2147483648K / 64K) / 8) + = 4194304B = 4MiB. + +QEMU uses these bitmaps when making incremental backups to know which sections +of the file to copy out. They are not enabled by default and must be +explicitly added in order to begin tracking writes. + +Bitmaps can be created at any time and can be attached to any arbitrary block +node in the storage graph, but are most useful conceptually when attached to +the root node attached to the guest's storage device model. + +That is to say: It's likely most useful to track the guest's writes to disk, +but you could theoretically track things like qcow2 metadata changes by +attaching the bitmap elsewhere in the storage graph. This is beyond the scope +of this document. + +QEMU supports persisting these bitmaps to disk via the qcow2 image format. +Bitmaps which are stored or loaded in this way are called "persistent", +whereas bitmaps that are not are called "transient". + +QEMU also supports the migration of both transient bitmaps (tracking any +arbitrary image format) or persistent bitmaps (qcow2) via live migration. + +Supported Image Formats +----------------------- + +QEMU supports all documented features below on the qcow2 image format. + +However, qcow2 is only strictly necessary for the persistence feature, which +writes bitmap data to disk upon close. If persistence is not required for a +specific use case, all bitmap features excepting persistence are available for +any arbitrary image format. + +For example, Dirty Bitmaps can be combined with the 'raw' image format, but +any changes to the bitmap will be discarded upon exit. + +.. warning:: Transient bitmaps will not be saved on QEMU exit! Persistent + bitmaps are available only on qcow2 images. + Dirty Bitmap Names ------------------ -- A dirty bitmap's name is unique to the node, but bitmaps attached to - different nodes can share the same name. +Bitmap objects need a method to reference them in the API. All API-created and +managed bitmaps have a human-readable name chosen by the user at creation +time. -- Dirty bitmaps created for internal use by QEMU may be anonymous and - have no name, but any user-created bitmaps must have a name. There - can be any number of anonymous bitmaps per node. +- A bitmap's name is unique to the node, but bitmaps attached to different + nodes can share the same name. Therefore, all bitmaps are addressed via + their (node, name) pair. -- The name of a user-created bitmap must not be empty (""). +- The name of a user-created bitmap cannot be empty (""). -Bitmap Modes ------------- +- Transient bitmaps can have JSON unicode names that are effectively not + length limited. (QMP protocol may restrict messages to less than 64MiB.) + +- Persistent storage formats may impose their own requirements on bitmap names + and namespaces. Presently, only qcow2 supports persistent bitmaps. See + docs/interop/qcow2.txt for more details on restrictions. Notably: + + - qcow2 bitmap names are limited to between 1 and 1023 bytes long. + + - No two bitmaps saved to the same qcow2 file may share the same name. + +- QEMU occasionally uses bitmaps for internal use which have no name. They are + hidden from API query calls, cannot be manipulated by the external API, are + never persistent, nor ever migrated. + +Bitmap Status +------------- + +Dirty Bitmap objects can be queried with the QMP command `query-block +<qemu-qmp-ref.html#index-query_002dblock>`_, and are visible via the +`BlockDirtyInfo <qemu-qmp-ref.html#index-BlockDirtyInfo>`_ QAPI structure. + +This struct shows the name, granularity, and dirty byte count for each bitmap. +Additionally, it shows several boolean status indicators: + +- ``recording``: This bitmap is recording writes. +- ``busy``: This bitmap is in-use by an operation. +- ``persistent``: This bitmap is a persistent type. +- ``inconsistent``: This bitmap is corrupted and cannot be used. + +The ``+busy`` status prohibits you from deleting, clearing, or otherwise +modifying a bitmap, and happens when the bitmap is being used for a backup +operation or is in the process of being loaded from a migration. Many of the +commands documented below will refuse to work on such bitmaps. + +The ``+inconsistent`` status similarly prohibits almost all operations, +notably allowing only the ``block-dirty-bitmap-remove`` operation. + +There is also a deprecated ``status`` field of type `DirtyBitmapStatus +<qemu-qmp-ref.html#index-DirtyBitmapStatus>`_. A bitmap historically had +five visible states: + + #. ``Frozen``: This bitmap is currently in-use by an operation and is + immutable. It can't be deleted, renamed, reset, etc. + + (This is now ``+busy``.) + + #. ``Disabled``: This bitmap is not recording new writes. + + (This is now ``-recording -busy``.) + + #. ``Active``: This bitmap is recording new writes. + + (This is now ``+recording -busy``.) -- A bitmap can be "frozen," which means that it is currently in-use by - a backup operation and cannot be deleted, renamed, written to, reset, - etc. + #. ``Locked``: This bitmap is in-use by an operation, and is immutable. + The difference from "Frozen" was primarily implementation details. -- The normal operating mode for a bitmap is "active." + (This is now ``+busy``.) + + #. ``Inconsistent``: This persistent bitmap was not saved to disk + correctly, and can no longer be used. It remains in memory to serve as + an indicator of failure. + + (This is now ``+inconsistent``.) + +These states are directly replaced by the status indicators and should not be +used. The difference between ``Frozen`` and ``Locked`` is an implementation +detail and should not be relevant to external users. Basic QMP Usage --------------- +The primary interface to manipulating bitmap objects is via the QMP +interface. If you are not familiar, see docs/interop/qmp-intro.txt for a broad +overview, and `qemu-qmp-ref <qemu-qmp-ref.html>`_ for a full reference of all +QMP commands. + Supported Commands ~~~~~~~~~~~~~~~~~~ +There are six primary bitmap-management API commands: + - ``block-dirty-bitmap-add`` - ``block-dirty-bitmap-remove`` - ``block-dirty-bitmap-clear`` +- ``block-dirty-bitmap-disable`` +- ``block-dirty-bitmap-enable`` +- ``block-dirty-bitmap-merge`` -Creation -~~~~~~~~ +And one related query command: -- To create a new bitmap, enabled, on the drive with id=drive0: +- ``query-block`` -.. code:: json +Creation: block-dirty-bitmap-add +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - { "execute": "block-dirty-bitmap-add", - "arguments": { - "node": "drive0", - "name": "bitmap0" - } - } +`block-dirty-bitmap-add +<qemu-qmp-ref.html#index-block_002ddirty_002dbitmap_002dadd>`_: -- This bitmap will have a default granularity that matches the cluster - size of its associated drive, if available, clamped to between [4KiB, - 64KiB]. The current default for qcow2 is 64KiB. +Creates a new bitmap that tracks writes to the specified node. granularity, +persistence, and recording state can be adjusted at creation time. -- To create a new bitmap that tracks changes in 32KiB segments: +.. admonition:: Example -.. code:: json + to create a new, actively recording persistent bitmap: - { "execute": "block-dirty-bitmap-add", - "arguments": { - "node": "drive0", - "name": "bitmap0", - "granularity": 32768 - } - } + .. code:: json -Deletion -~~~~~~~~ + -> { "execute": "block-dirty-bitmap-add", + "arguments": { + "node": "drive0", + "name": "bitmap0", + "persistent": true, + } + } -- Bitmaps that are frozen cannot be deleted. + <- { "return": {} } -- Deleting the bitmap does not impact any other bitmaps attached to the - same node, nor does it affect any backups already created from this - node. +- This bitmap will have a default granularity that matches the cluster size of + its associated drive, if available, clamped to between [4KiB, 64KiB]. The + current default for qcow2 is 64KiB. -- Because bitmaps are only unique to the node to which they are - attached, you must specify the node/drive name here, too. +.. admonition:: Example -.. code:: json + To create a new, disabled (``-recording``), transient bitmap that tracks + changes in 32KiB segments: - { "execute": "block-dirty-bitmap-remove", - "arguments": { - "node": "drive0", - "name": "bitmap0" - } - } + .. code:: json -Resetting -~~~~~~~~~ + -> { "execute": "block-dirty-bitmap-add", + "arguments": { + "node": "drive0", + "name": "bitmap1", + "granularity": 32768, + "disabled": true + } + } -- Resetting a bitmap will clear all information it holds. + <- { "return": {} } -- An incremental backup created from an empty bitmap will copy no data, - as if nothing has changed. +Deletion: block-dirty-bitmap-remove +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -.. code:: json +`block-dirty-bitmap-remove +<qemu-qmp-ref.html#index-block_002ddirty_002dbitmap_002dremove>`_: + +Deletes a bitmap. Bitmaps that are ``+busy`` cannot be removed. + +- Deleting a bitmap does not impact any other bitmaps attached to the same + node, nor does it affect any backups already created from this bitmap or + node. + +- Because bitmaps are only unique to the node to which they are attached, you + must specify the node/drive name here, too. + +- Deleting a persistent bitmap will remove it from the qcow2 file. + +.. admonition:: Example + + Remove a bitmap named ``bitmap0`` from node ``drive0``: + + .. code:: json + + -> { "execute": "block-dirty-bitmap-remove", + "arguments": { + "node": "drive0", + "name": "bitmap0" + } + } + + <- { "return": {} } + +Resetting: block-dirty-bitmap-clear +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +`block-dirty-bitmap-clear +<qemu-qmp-ref.html#index-block_002ddirty_002dbitmap_002dclear>`_: + +Clears all dirty bits from a bitmap. ``+busy`` bitmaps cannot be cleared. + +- An incremental backup created from an empty bitmap will copy no data, as if + nothing has changed. + +.. admonition:: Example + + Clear all dirty bits from bitmap ``bitmap0`` on node ``drive0``: + + .. code:: json + + -> { "execute": "block-dirty-bitmap-clear", + "arguments": { + "node": "drive0", + "name": "bitmap0" + } + } + + <- { "return": {} } + +Enabling: block-dirty-bitmap-enable +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +`block-dirty-bitmap-enable +<qemu-qmp-ref.html#index-block_002ddirty_002dbitmap_002denable>`_: - { "execute": "block-dirty-bitmap-clear", - "arguments": { - "node": "drive0", - "name": "bitmap0" - } - } +"Enables" a bitmap, setting the ``recording`` bit to true, causing writes to +begin being recorded. ``+busy`` bitmaps cannot be enabled. + +- Bitmaps default to being enabled when created, unless configured otherwise. + +- Persistent enabled bitmaps will remember their ``+recording`` status on + load. + +.. admonition:: Example + + To set ``+recording`` on bitmap ``bitmap0`` on node ``drive0``: + + .. code:: json + + -> { "execute": "block-dirty-bitmap-enable", + "arguments": { + "node": "drive0", + "name": "bitmap0" + } + } + + <- { "return": {} } + +Enabling: block-dirty-bitmap-disable +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +`block-dirty-bitmap-disable +<qemu-qmp-ref.html#index-block_002ddirty_002dbitmap_002ddisable>`_: + +"Disables" a bitmap, setting the ``recording`` bit to false, causing further +writes to begin being ignored. ``+busy`` bitmaps cannot be disabled. + +.. warning:: + + This is potentially dangerous: QEMU makes no effort to stop any writes if + there are disabled bitmaps on a node, and will not mark any disabled bitmaps + as ``+inconsistent`` if any such writes do happen. Backups made from such + bitmaps will not be able to be used to reconstruct a coherent image. + +- Disabling a bitmap may be useful for examining which sectors of a disk + changed during a specific time period, or for explicit management of + differential backup windows. + +- Persistent disabled bitmaps will remember their ``-recording`` status on + load. + +.. admonition:: Example + + To set ``-recording`` on bitmap ``bitmap0`` on node ``drive0``: + + .. code:: json + + -> { "execute": "block-dirty-bitmap-disable", + "arguments": { + "node": "drive0", + "name": "bitmap0" + } + } + + <- { "return": {} } + +Merging, Copying: block-dirty-bitmap-merge +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +`block-dirty-bitmap-merge +<qemu-qmp-ref.html#index-block_002ddirty_002dbitmap_002dmerge>`_: + +Merges one or more bitmaps into a target bitmap. For any segment that is dirty +in any one source bitmap, the target bitmap will mark that segment dirty. + +- Merge takes one or more bitmaps as a source and merges them together into a + single destination, such that any segment marked as dirty in any source + bitmap(s) will be marked dirty in the destination bitmap. + +- Merge does not create the destination bitmap if it does not exist. A blank + bitmap can be created beforehand to achieve the same effect. + +- The destination is not cleared prior to merge, so subsequent merge + operations will continue to cumulatively mark more segments as dirty. + +- If the merge operation should fail, the destination bitmap is guaranteed to + be unmodified. The operation may fail if the source or destination bitmaps + are busy, or have different granularities. + +- Bitmaps can only be merged on the same node. There is only one "node" + argument, so all bitmaps must be attached to that same node. + +- Copy can be achieved by merging from a single source to an empty + destination. + +.. admonition:: Example + + Merge the data from ``bitmap0`` into the bitmap ``new_bitmap`` on node + ``drive0``. If ``new_bitmap`` was empty prior to this command, this achieves + a copy. + + .. code:: json + + -> { "execute": "block-dirty-bitmap-merge", + "arguments": { + "node": "drive0", + "target": "new_bitmap", + "bitmaps: [ "bitmap0" ] + } + } + + <- { "return": {} } + +Querying: query-block +~~~~~~~~~~~~~~~~~~~~~ + +`query-block +<qemu-qmp-ref.html#index-query_002dblock>`_: + +Not strictly a bitmaps command, but will return information about any bitmaps +attached to nodes serving as the root for guest devices. + +- The "inconsistent" bit will not appear when it is false, appearing only when + the value is true to indicate there is a problem. + +.. admonition:: Example + + Query the block sub-system of QEMU. The following json has trimmed irrelevant + keys from the response to highlight only the bitmap-relevant portions of the + API. This result highlights a bitmap ``bitmap0`` attached to the root node of + device ``drive0``. + + .. code:: json + + -> { + "execute": "query-block", + "arguments": {} + } + + <- { + "return": [ { + "dirty-bitmaps": [ { + "status": "active", + "count": 0, + "busy": false, + "name": "bitmap0", + "persistent": false, + "recording": true, + "granularity": 65536 + } ], + "device": "drive0", + } ] + } + +Bitmap Persistence +------------------ + +As outlined in `Supported Image Formats`_, QEMU can persist bitmaps to qcow2 +files. Demonstrated in `Creation: block-dirty-bitmap-add`_, passing +``persistent: true`` to ``block-dirty-bitmap-add`` will persist that bitmap to +disk. + +Persistent bitmaps will be automatically loaded into memory upon load, and +will be written back to disk upon close. Their usage should be mostly +transparent. + +However, if QEMU does not get a chance to close the file cleanly, the bitmap +will be marked as ``+inconsistent`` at next load and considered unsafe to use +for any operation. At this point, the only valid operation on such bitmaps is +``block-dirty-bitmap-remove``. + +Losing a bitmap in this way does not invalidate any existing backups that have +been made from this bitmap, but no further backups will be able to be issued +for this chain. Transactions ------------ +Transactions are a QMP feature that allows you to submit multiple QMP commands +at once, being guaranteed that they will all succeed or fail atomically, +together. The interaction of bitmaps and transactions are demonstrated below. + +See `transaction <qemu-qmp.ref.html#index-transaction>`_ in the QMP reference +for more details. + Justification ~~~~~~~~~~~~~ -Bitmaps can be safely modified when the VM is paused or halted by using -the basic QMP commands. For instance, you might perform the following -actions: +Bitmaps can generally be modified at any time, but certain operations often +only make sense when paired directly with other commands. When a VM is paused, +it's easy to ensure that no guest writes occur between individual QMP +commands. When a VM is running, this is difficult to accomplish with +individual QMP commands that may allow guest writes to occur inbetween each +command. -1. Boot the VM in a paused state. -2. Create a full drive backup of drive0. -3. Create a new bitmap attached to drive0. -4. Resume execution of the VM. -5. Incremental backups are ready to be created. +For example, using only individual QMP commands, we could: -At this point, the bitmap and drive backup would be correctly in sync, -and incremental backups made from this point forward would be correctly -aligned to the full drive backup. +#. Boot the VM in a paused state. +#. Create a full drive backup of drive0. +#. Create a new bitmap attached to drive0, confident that nothing has been + written to drive0 in the meantime. +#. Resume execution of the VM. +#. At a later point, issue incremental backups from ``bitmap0``. -This is not particularly useful if we decide we want to start -incremental backups after the VM has been running for a while, for which -we will need to perform actions such as the following: +At this point, the bitmap and drive backup would be correctly in sync, and +incremental backups made from this point forward would be correctly aligned to +the full drive backup. -1. Boot the VM and begin execution. -2. Using a single transaction, perform the following operations: +This is not particularly useful if we decide we want to start incremental +backups after the VM has been running for a while, for which we would want to +perform actions such as the following: + +#. Boot the VM and begin execution. +#. Using a single transaction, perform the following operations: - Create ``bitmap0``. - Create a full drive backup of ``drive0``. -3. Incremental backups are now ready to be created. +#. At a later point, issue incremental backups from ``bitmap0``. + +.. note:: As a consideration, if ``bitmap0`` is created prior to the full + drive backup, incremental backups can still be authored from this + bitmap, but they will copy extra segments reflecting writes that + occurred prior to the backup operation. Transactions allow us to + narrow critical points in time to reduce waste, or, in the other + direction, to ensure that no segments are omitted. Supported Bitmap Transactions ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ - ``block-dirty-bitmap-add`` - ``block-dirty-bitmap-clear`` +- ``block-dirty-bitmap-enable`` +- ``block-dirty-bitmap-disable`` +- ``block-dirty-bitmap-merge`` -The usages are identical to their respective QMP commands, but see below -for examples. +The usages for these commands are identical to their respective QMP commands, +but see the sections below for concrete examples. -Example: New Incremental Backup -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Incremental Backups - Push Model +-------------------------------- -As outlined in the justification, perhaps we want to create a new -incremental backup chain attached to a drive. +Incremental backups are simply partial disk images that can be combined with +other partial disk images on top of a base image to reconstruct a full backup +from the point in time at which the incremental backup was issued. -.. code:: json +The "Push Model" here references the fact that QEMU is "pushing" the modified +blocks out to a destination. We will be using the `drive-backup +<qemu-qmp-ref.html#index-drive_002dbackup>`_ and `blockdev-backup +<qemu-qmp-ref.html#index-blockdev_002dbackup>`_ QMP commands to create both +full and incremental backups. - { "execute": "transaction", - "arguments": { - "actions": [ - {"type": "block-dirty-bitmap-add", - "data": {"node": "drive0", "name": "bitmap0"} }, - {"type": "drive-backup", - "data": {"device": "drive0", "target": "/path/to/full_backup.img", - "sync": "full", "format": "qcow2"} } - ] - } - } +Both of these commands are jobs, which have their own QMP API for querying and +management documented in `Background jobs +<qemu-qmp-ref.html#Background-jobs>`_. Example: New Incremental Backup Anchor Point ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -Maybe we just want to create a new full backup with an existing bitmap -and want to reset the bitmap to track the new chain. +As outlined in the Transactions - `Justification`_ section, perhaps we want to +create a new incremental backup chain attached to a drive. + +This example creates a new, full backup of "drive0" and accompanies it with a +new, empty bitmap that records writes from this point in time forward. + +.. note:: Any new writes that happen after this command is issued, even while + the backup job runs, will be written locally and not to the backup + destination. These writes will be recorded in the bitmap + accordingly. + +.. code:: json + + -> { + "execute": "transaction", + "arguments": { + "actions": [ + { + "type": "block-dirty-bitmap-add", + "data": { + "node": "drive0", + "name": "bitmap0" + } + }, + { + "type": "drive-backup", + "data": { + "device": "drive0", + "target": "/path/to/drive0.full.qcow2", + "sync": "full", + "format": "qcow2" + } + } + ] + } + } + + <- { "return": {} } + + <- { + "timestamp": { + "seconds": 1555436945, + "microseconds": 179620 + }, + "data": { + "status": "created", + "id": "drive0" + }, + "event": "JOB_STATUS_CHANGE" + } + + ... + + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 68719476736, + "offset": 68719476736 + }, + "event": "BLOCK_JOB_COMPLETED" + } + + <- { + "timestamp": {...}, + "data": { + "status": "concluded", + "id": "drive0" + }, + "event": "JOB_STATUS_CHANGE" + } + + <- { + "timestamp": {...}, + "data": { + "status": "null", + "id": "drive0" + }, + "event": "JOB_STATUS_CHANGE" + } + +A full explanation of the job transition semantics and the JOB_STATUS_CHANGE +event are beyond the scope of this document and will be omitted in all +subsequent examples; above, several more events have been omitted for brevity. + +.. note:: Subsequent examples will omit all events except BLOCK_JOB_COMPLETED + except where necessary to illustrate workflow differences. + + Omitted events and json objects will be represented by ellipses: + ``...`` + +Example: Resetting an Incremental Backup Anchor Point +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +If we want to start a new backup chain with an existing bitmap, we can also +use a transaction to reset the bitmap while making a new full backup: .. code:: json - { "execute": "transaction", - "arguments": { - "actions": [ - {"type": "block-dirty-bitmap-clear", - "data": {"node": "drive0", "name": "bitmap0"} }, - {"type": "drive-backup", - "data": {"device": "drive0", "target": "/path/to/new_full_backup.img", - "sync": "full", "format": "qcow2"} } - ] - } - } - -Incremental Backups -------------------- - -The star of the show. - -**Nota Bene!** Only incremental backups of entire drives are supported -for now. So despite the fact that you can attach a bitmap to any -arbitrary node, they are only currently useful when attached to the root -node. This is because drive-backup only supports drives/devices instead -of arbitrary nodes. + -> { + "execute": "transaction", + "arguments": { + "actions": [ + { + "type": "block-dirty-bitmap-clear", + "data": { + "node": "drive0", + "name": "bitmap0" + } + }, + { + "type": "drive-backup", + "data": { + "device": "drive0", + "target": "/path/to/drive0.new_full.qcow2", + "sync": "full", + "format": "qcow2" + } + } + ] + } + } + + <- { "return": {} } + + ... + + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 68719476736, + "offset": 68719476736 + }, + "event": "BLOCK_JOB_COMPLETED" + } + + ... + +The result of this example is identical to the first, but we clear an existing +bitmap instead of adding a new one. + +.. tip:: In both of these examples, "bitmap0" is tied conceptually to the + creation of new, full backups. This relationship is not saved or + remembered by QEMU; it is up to the operator or management layer to + remember which bitmaps are associated with which backups. Example: First Incremental Backup ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -1. Create a full backup and sync it to the dirty bitmap, as in the - transactional examples above; or with the VM offline, manually create - a full copy and then create a new bitmap before the VM begins - execution. +#. Create a full backup and sync it to a dirty bitmap using any method: - - Let's assume the full backup is named ``full_backup.img``. - - Let's assume the bitmap you created is ``bitmap0`` attached to - ``drive0``. + - Either of the two live backup method demonstrated above, + - Using QMP commands with the VM paused as in the `Justification`_ section, + or + - With the VM offline, manually copy the image and start the VM in a paused + state, careful to add a new bitmap before the VM begins execution. -2. Create a destination image for the incremental backup that utilizes - the full backup as a backing image. + Whichever method is chosen, let's assume that at the end of this step: - - Let's assume the new incremental image is named - ``incremental.0.img``. + - The full backup is named ``drive0.full.qcow2``. + - The bitmap we created is named ``bitmap0``, attached to ``drive0``. + +#. Create a destination image for the incremental backup that utilizes the + full backup as a backing image. + + - Let's assume the new incremental image is named ``drive0.inc0.qcow2``: .. code:: bash - $ qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2 + $ qemu-img create -f qcow2 drive0.inc0.qcow2 \ + -b drive0.full.qcow2 -F qcow2 -3. Issue the incremental backup command: +#. Issue an incremental backup command: .. code:: json - { "execute": "drive-backup", + -> { + "execute": "drive-backup", "arguments": { "device": "drive0", "bitmap": "bitmap0", - "target": "incremental.0.img", + "target": "drive0.inc0.qcow2", "format": "qcow2", "sync": "incremental", "mode": "existing" } } + <- { "return": {} } + + ... + + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 68719476736, + "offset": 68719476736 + }, + "event": "BLOCK_JOB_COMPLETED" + } + + ... + +This copies any blocks modified since the full backup was created into the +``drive0.inc0.qcow2`` file. During the operation, ``bitmap0`` is marked +``+busy``. If the operation is successful, ``bitmap0`` will be cleared to +reflect the "incremental" backup regimen, which only copies out new changes +from each incremental backup. + +.. note:: Any new writes that occur after the backup operation starts do not + get copied to the destination. The backup's "point in time" is when + the backup starts, not when it ends. These writes are recorded in a + special bitmap that gets re-added to bitmap0 when the backup ends so + that the next incremental backup can copy them out. + Example: Second Incremental Backup ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -1. Create a new destination image for the incremental backup that points - to the previous one, e.g.: ``incremental.1.img`` +#. Create a new destination image for the incremental backup that points to + the previous one, e.g.: ``drive0.inc1.qcow2`` .. code:: bash - $ qemu-img create -f qcow2 incremental.1.img -b incremental.0.img -F qcow2 + $ qemu-img create -f qcow2 drive0.inc1.qcow2 \ + -b drive0.inc0.qcow2 -F qcow2 -2. Issue a new incremental backup command. The only difference here is - that we have changed the target image below. +#. Issue a new incremental backup command. The only difference here is that we + have changed the target image below. .. code:: json - { "execute": "drive-backup", + -> { + "execute": "drive-backup", "arguments": { "device": "drive0", "bitmap": "bitmap0", - "target": "incremental.1.img", + "target": "drive0.inc1.qcow2", "format": "qcow2", "sync": "incremental", "mode": "existing" } } -Errors ------- + <- { "return": {} } + + ... + + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 68719476736, + "offset": 68719476736 + }, + "event": "BLOCK_JOB_COMPLETED" + } + + ... + +Because the first incremental backup from the previous example completed +successfully, ``bitmap0`` was synchronized with ``drive0.inc0.qcow2``. Here, +we use ``bitmap0`` again to create a new incremental backup that targets the +previous one, creating a chain of three images: + +.. admonition:: Diagram + + .. code:: text + + +-------------------+ +-------------------+ +-------------------+ + | drive0.full.qcow2 |<--| drive0.inc0.qcow2 |<--| drive0.inc1.qcow2 | + +-------------------+ +-------------------+ +-------------------+ + +Each new incremental backup re-synchronizes the bitmap to the latest backup +authored, allowing a user to continue to "consume" it to create new backups on +top of an existing chain. + +In the above diagram, neither drive0.inc1.qcow2 nor drive0.inc0.qcow2 are +complete images by themselves, but rely on their backing chain to reconstruct +a full image. The dependency terminates with each full backup. + +Each backup in this chain remains independent, and is unchanged by new entries +made later in the chain. For instance, drive0.inc0.qcow2 remains a perfectly +valid backup of the disk as it was when that backup was issued. + +Example: Incremental Push Backups without Backing Files +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Backup images are best kept off-site, so we often will not have the preceding +backups in a chain available to link against. This is not a problem at backup +time; we simply do not set the backing image when creating the destination +image: + +#. Create a new destination image with no backing file set. We will need to + specify the size of the base image, because the backing file isn't + available for QEMU to use to determine it. + + .. code:: bash + + $ qemu-img create -f qcow2 drive0.inc2.qcow2 64G + + .. note:: Alternatively, you can omit ``mode: "existing"`` from the push + backup commands to have QEMU create an image without a backing + file for you, but you lose control over format options like + compatibility and preallocation presets. + +#. Issue a new incremental backup command. Apart from the new destination + image, there is no difference from the last two examples. + + .. code:: json + + -> { + "execute": "drive-backup", + "arguments": { + "device": "drive0", + "bitmap": "bitmap0", + "target": "drive0.inc2.qcow2", + "format": "qcow2", + "sync": "incremental", + "mode": "existing" + } + } + + <- { "return": {} } + + ... + + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 68719476736, + "offset": 68719476736 + }, + "event": "BLOCK_JOB_COMPLETED" + } + + ... + +The only difference from the perspective of the user is that you will need to +set the backing image when attempting to restore the backup: + +.. code:: bash + + $ qemu-img rebase drive0.inc2.qcow2 \ + -u -b drive0.inc1.qcow2 + +This uses the "unsafe" rebase mode to simply set the backing file to a file +that isn't present. + +It is also possible to use ``--image-opts`` to specify the entire backing +chain by hand as an ephemeral property at runtime, but that is beyond the +scope of this document. + +Example: Multi-drive Incremental Backup +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Assume we have a VM with two drives, "drive0" and "drive1" and we wish to back +both of them up such that the two backups represent the same crash-consistent +point in time. + +#. For each drive, create an empty image: + + .. code:: bash + + $ qemu-img create -f qcow2 drive0.full.qcow2 64G + $ qemu-img create -f qcow2 drive1.full.qcow2 64G + +#. Create a full (anchor) backup for each drive, with accompanying bitmaps: + + .. code:: json + + -> { + "execute": "transaction", + "arguments": { + "actions": [ + { + "type": "block-dirty-bitmap-add", + "data": { + "node": "drive0", + "name": "bitmap0" + } + }, + { + "type": "block-dirty-bitmap-add", + "data": { + "node": "drive1", + "name": "bitmap0" + } + }, + { + "type": "drive-backup", + "data": { + "device": "drive0", + "target": "/path/to/drive0.full.qcow2", + "sync": "full", + "format": "qcow2" + } + }, + { + "type": "drive-backup", + "data": { + "device": "drive1", + "target": "/path/to/drive1.full.qcow2", + "sync": "full", + "format": "qcow2" + } + } + ] + } + } + + <- { "return": {} } + + ... + + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 68719476736, + "offset": 68719476736 + }, + "event": "BLOCK_JOB_COMPLETED" + } + + ... + + <- { + "timestamp": {...}, + "data": { + "device": "drive1", + "type": "backup", + "speed": 0, + "len": 68719476736, + "offset": 68719476736 + }, + "event": "BLOCK_JOB_COMPLETED" + } + + ... + +#. Later, create new destination images for each of the incremental backups + that point to their respective full backups: + + .. code:: bash + + $ qemu-img create -f qcow2 drive0.inc0.qcow2 \ + -b drive0.full.qcow2 -F qcow2 + $ qemu-img create -f qcow2 drive1.inc0.qcow2 \ + -b drive1.full.qcow2 -F qcow2 + +#. Issue a multi-drive incremental push backup transaction: + + .. code:: json + + -> { + "execute": "transaction", + "arguments": { + "actions": [ + { + "type": "drive-backup", + "data": { + "device": "drive0", + "bitmap": "bitmap0", + "format": "qcow2", + "mode": "existing", + "sync": "incremental", + "target": "drive0.inc0.qcow2" + } + }, + { + "type": "drive-backup", + "data": { + "device": "drive1", + "bitmap": "bitmap0", + "format": "qcow2", + "mode": "existing", + "sync": "incremental", + "target": "drive1.inc0.qcow2" + } + }, + ] + } + } + + <- { "return": {} } + + ... + + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 68719476736, + "offset": 68719476736 + }, + "event": "BLOCK_JOB_COMPLETED" + } + + ... + + <- { + "timestamp": {...}, + "data": { + "device": "drive1", + "type": "backup", + "speed": 0, + "len": 68719476736, + "offset": 68719476736 + }, + "event": "BLOCK_JOB_COMPLETED" + } + + ... -- In the event of an error that occurs after a backup job is - successfully launched, either by a direct QMP command or a QMP - transaction, the user will receive a ``BLOCK_JOB_COMPLETE`` event with - a failure message, accompanied by a ``BLOCK_JOB_ERROR`` event. +Push Backup Errors & Recovery +----------------------------- -- In the case of an event being cancelled, the user will receive a - ``BLOCK_JOB_CANCELLED`` event instead of a pair of COMPLETE and ERROR - events. +In the event of an error that occurs after a push backup job is successfully +launched, either by an individual QMP command or a QMP transaction, the user +will receive a ``BLOCK_JOB_COMPLETE`` event with a failure message, +accompanied by a ``BLOCK_JOB_ERROR`` event. -- In either case, the incremental backup data contained within the - bitmap is safely rolled back, and the data within the bitmap is not - lost. The image file created for the failed attempt can be safely - deleted. +In the case of a job being cancelled, the user will receive a +``BLOCK_JOB_CANCELLED`` event instead of a pair of COMPLETE and ERROR +events. -- Once the underlying problem is fixed (e.g. more storage space is - freed up), you can simply retry the incremental backup command with - the same bitmap. +In either failure case, the bitmap used for the failed operation is not +cleared. It will contain all of the dirty bits it did at the start of the +operation, plus any new bits that got marked during the operation. -Example -~~~~~~~ +Effectively, the "point in time" that a bitmap is recording differences +against is kept at the issuance of the last successful incremental backup, +instead of being moved forward to the start of this now-failed backup. -1. Create a target image: +Once the underlying problem is addressed (e.g. more storage space is allocated +on the destination), the incremental backup command can be retried with the +same bitmap. + +Example: Individual Failures +~~~~~~~~~~~~~~~~~~~~~~~~~~~~ + +Incremental Push Backup jobs that fail individually behave simply as +described above. This example demonstrates the single-job failure case: + +#. Create a target image: .. code:: bash - $ qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2 + $ qemu-img create -f qcow2 drive0.inc0.qcow2 \ + -b drive0.full.qcow2 -F qcow2 -2. Attempt to create an incremental backup via QMP: +#. Attempt to create an incremental backup via QMP: .. code:: json - { "execute": "drive-backup", + -> { + "execute": "drive-backup", "arguments": { "device": "drive0", "bitmap": "bitmap0", - "target": "incremental.0.img", + "target": "drive0.inc0.qcow2", "format": "qcow2", "sync": "incremental", "mode": "existing" } } -3. Receive an event notifying us of failure: + <- { "return": {} } + +#. Receive a pair of events indicating failure: .. code:: json - { "timestamp": { "seconds": 1424709442, "microseconds": 844524 }, - "data": { "speed": 0, "offset": 0, "len": 67108864, - "error": "No space left on device", - "device": "drive1", "type": "backup" }, - "event": "BLOCK_JOB_COMPLETED" } + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "action": "report", + "operation": "write" + }, + "event": "BLOCK_JOB_ERROR" + } + + <- { + "timestamp": {...}, + "data": { + "speed": 0, + "offset": 0, + "len": 67108864, + "error": "No space left on device", + "device": "drive0", + "type": "backup" + }, + "event": "BLOCK_JOB_COMPLETED" + } -4. Delete the failed incremental, and re-create the image. +#. Delete the failed image, and re-create it. .. code:: bash - $ rm incremental.0.img - $ qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2 + $ rm drive0.inc0.qcow2 + $ qemu-img create -f qcow2 drive0.inc0.qcow2 \ + -b drive0.full.qcow2 -F qcow2 -5. Retry the command after fixing the underlying problem, such as +#. Retry the command after fixing the underlying problem, such as freeing up space on the backup volume: .. code:: json - { "execute": "drive-backup", + -> { + "execute": "drive-backup", "arguments": { "device": "drive0", "bitmap": "bitmap0", - "target": "incremental.0.img", + "target": "drive0.inc0.qcow2", "format": "qcow2", "sync": "incremental", "mode": "existing" } } -6. Receive confirmation that the job completed successfully: + <- { "return": {} } + +#. Receive confirmation that the job completed successfully: .. code:: json - { "timestamp": { "seconds": 1424709668, "microseconds": 526525 }, - "data": { "device": "drive1", "type": "backup", - "speed": 0, "len": 67108864, "offset": 67108864}, - "event": "BLOCK_JOB_COMPLETED" } + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 67108864, + "offset": 67108864 + }, + "event": "BLOCK_JOB_COMPLETED" + } -Partial Transactional Failures -~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +Example: Partial Transactional Failures +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- Sometimes, a transaction will succeed in launching and return - success, but then later the backup jobs themselves may fail. It is - possible that a management application may have to deal with a - partial backup failure after a successful transaction. +QMP commands like `drive-backup <qemu-qmp-ref.html#index-drive_002dbackup>`_ +conceptually only start a job, and so transactions containing these commands +may succeed even if the job it created later fails. This might have surprising +interactions with notions of how a "transaction" ought to behave. -- If multiple backup jobs are specified in a single transaction, when - one of them fails, it will not interact with the other backup jobs in - any way. +This distinction means that on occasion, a transaction containing such job +launching commands may appear to succeed and return success, but later +individual jobs associated with the transaction may fail. It is possible that +a management application may have to deal with a partial backup failure after +a "successful" transaction. -- The job(s) that succeeded will clear the dirty bitmap associated with - the operation, but the job(s) that failed will not. It is not "safe" - to delete any incremental backups that were created successfully in - this scenario, even though others failed. +If multiple backup jobs are specified in a single transaction, if one of those +jobs fails, it will not interact with the other backup jobs in any way by +default. The job(s) that succeeded will clear the dirty bitmap associated with +the operation, but the job(s) that failed will not. It is therefore not safe +to delete any incremental backups that were created successfully in this +scenario, even though others failed. -Example -^^^^^^^ +This example illustrates a transaction with two backup jobs, where one fails +and one succeeds: -- QMP example highlighting two backup jobs: +#. Issue the transaction to start a backup of both drives. .. code:: json - { "execute": "transaction", + -> { + "execute": "transaction", "arguments": { "actions": [ - { "type": "drive-backup", - "data": { "device": "drive0", "bitmap": "bitmap0", - "format": "qcow2", "mode": "existing", - "sync": "incremental", "target": "d0-incr-1.qcow2" } }, - { "type": "drive-backup", - "data": { "device": "drive1", "bitmap": "bitmap1", - "format": "qcow2", "mode": "existing", - "sync": "incremental", "target": "d1-incr-1.qcow2" } }, - ] + { + "type": "drive-backup", + "data": { + "device": "drive0", + "bitmap": "bitmap0", + "format": "qcow2", + "mode": "existing", + "sync": "incremental", + "target": "drive0.inc0.qcow2" + } + }, + { + "type": "drive-backup", + "data": { + "device": "drive1", + "bitmap": "bitmap0", + "format": "qcow2", + "mode": "existing", + "sync": "incremental", + "target": "drive1.inc0.qcow2" + } + }] } } -- QMP example response, highlighting one success and one failure: +#. Receive notice that the Transaction was accepted, and jobs were + launched: - - Acknowledgement that the Transaction was accepted and jobs were - launched: + .. code:: json - .. code:: json + <- { "return": {} } - { "return": {} } +#. Receive notice that the first job has completed: - - Later, QEMU sends notice that the first job was completed: + .. code:: json - .. code:: json + <- { + "timestamp": {...}, + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 67108864, + "offset": 67108864 + }, + "event": "BLOCK_JOB_COMPLETED" + } - { "timestamp": { "seconds": 1447192343, "microseconds": 615698 }, - "data": { "device": "drive0", "type": "backup", - "speed": 0, "len": 67108864, "offset": 67108864 }, - "event": "BLOCK_JOB_COMPLETED" - } +#. Receive notice that the second job has failed: - - Later yet, QEMU sends notice that the second job has failed: + .. code:: json + + <- { + "timestamp": {...}, + "data": { + "device": "drive1", + "action": "report", + "operation": "read" + }, + "event": "BLOCK_JOB_ERROR" + } + + ... + + <- { + "timestamp": {...}, + "data": { + "speed": 0, + "offset": 0, + "len": 67108864, + "error": "Input/output error", + "device": "drive1", + "type": "backup" + }, + "event": "BLOCK_JOB_COMPLETED" + } - .. code:: json +At the conclusion of the above example, ``drive0.inc0.qcow2`` is valid and +must be kept, but ``drive1.inc0.qcow2`` is incomplete and should be +deleted. If a VM-wide incremental backup of all drives at a point-in-time is +to be made, new backups for both drives will need to be made, taking into +account that a new incremental backup for drive0 needs to be based on top of +``drive0.inc0.qcow2``. - { "timestamp": { "seconds": 1447192399, "microseconds": 683015 }, - "data": { "device": "drive1", "action": "report", - "operation": "read" }, - "event": "BLOCK_JOB_ERROR" } +For this example, an incremental backup for ``drive0`` was created, but not +for ``drive1``. The last VM-wide crash-consistent backup that is available in +this case is the full backup: - .. code:: json +.. code:: text - { "timestamp": { "seconds": 1447192399, "microseconds": - 685853 }, "data": { "speed": 0, "offset": 0, "len": 67108864, - "error": "Input/output error", "device": "drive1", "type": - "backup" }, "event": "BLOCK_JOB_COMPLETED" } + [drive0.full.qcow2] <-- [drive0.inc0.qcow2] + [drive1.full.qcow2] -- In the above example, ``d0-incr-1.qcow2`` is valid and must be kept, - but ``d1-incr-1.qcow2`` is invalid and should be deleted. If a VM-wide - incremental backup of all drives at a point-in-time is to be made, - new backups for both drives will need to be made, taking into account - that a new incremental backup for drive0 needs to be based on top of - ``d0-incr-1.qcow2``. +To repair this, issue a new incremental backup across both drives. The result +will be backup chains that resemble the following: -Grouped Completion Mode -~~~~~~~~~~~~~~~~~~~~~~~ +.. code:: text -- While jobs launched by transactions normally complete or fail on - their own, it is possible to instruct them to complete or fail - together as a group. + [drive0.full.qcow2] <-- [drive0.inc0.qcow2] <-- [drive0.inc1.qcow2] + [drive1.full.qcow2] <-------------------------- [drive1.inc1.qcow2] -- QMP transactions take an optional properties structure that can - affect the semantics of the transaction. +Example: Grouped Completion Mode +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ -- The "completion-mode" transaction property can be either "individual" - which is the default, legacy behavior described above, or "grouped," - a new behavior detailed below. +While jobs launched by transactions normally complete or fail individually, +it's possible to instruct them to complete or fail together as a group. QMP +transactions take an optional properties structure that can affect the +behavior of the transaction. -- Delayed Completion: In grouped completion mode, no jobs will report - success until all jobs are ready to report success. +The ``completion-mode`` transaction property can be either ``individual`` +which is the default legacy behavior described above, or ``grouped``, detailed +below. -- Grouped failure: If any job fails in grouped completion mode, all - remaining jobs will be cancelled. Any incremental backups will - restore their dirty bitmap objects as if no backup command was ever - issued. +In ``grouped`` completion mode, no jobs will report success until all jobs are +ready to report success. If any job fails, all other jobs will be cancelled. - - Regardless of if QEMU reports a particular incremental backup job - as CANCELLED or as an ERROR, the in-memory bitmap will be - restored. +Regardless of if a participating incremental backup job failed or was +cancelled, their associated bitmaps will all be held at their existing +points-in-time, as in individual failure cases. -Example -^^^^^^^ +Here's the same multi-drive backup scenario from `Example: Partial +Transactional Failures`_, but with the ``grouped`` completion-mode property +applied: -- Here's the same example scenario from above with the new property: +#. Issue the multi-drive incremental backup transaction: .. code:: json - { "execute": "transaction", + -> { + "execute": "transaction", "arguments": { - "actions": [ - { "type": "drive-backup", - "data": { "device": "drive0", "bitmap": "bitmap0", - "format": "qcow2", "mode": "existing", - "sync": "incremental", "target": "d0-incr-1.qcow2" } }, - { "type": "drive-backup", - "data": { "device": "drive1", "bitmap": "bitmap1", - "format": "qcow2", "mode": "existing", - "sync": "incremental", "target": "d1-incr-1.qcow2" } }, - ], "properties": { "completion-mode": "grouped" - } + }, + "actions": [ + { + "type": "drive-backup", + "data": { + "device": "drive0", + "bitmap": "bitmap0", + "format": "qcow2", + "mode": "existing", + "sync": "incremental", + "target": "drive0.inc0.qcow2" + } + }, + { + "type": "drive-backup", + "data": { + "device": "drive1", + "bitmap": "bitmap0", + "format": "qcow2", + "mode": "existing", + "sync": "incremental", + "target": "drive1.inc0.qcow2" + } + }] } } -- QMP example response, highlighting a failure for ``drive2``: +#. Receive notice that the Transaction was accepted, and jobs were launched: - - Acknowledgement that the Transaction was accepted and jobs were - launched: + .. code:: json + + <- { "return": {} } - .. code:: json +#. Receive notification that the backup job for ``drive1`` has failed: - { "return": {} } + .. code:: json - - Later, QEMU sends notice that the second job has errored out, but - that the first job was also cancelled: + <- { + "timestamp": {...}, + "data": { + "device": "drive1", + "action": "report", + "operation": "read" + }, + "event": "BLOCK_JOB_ERROR" + } - .. code:: json + <- { + "timestamp": {...}, + "data": { + "speed": 0, + "offset": 0, + "len": 67108864, + "error": "Input/output error", + "device": "drive1", + "type": "backup" + }, + "event": "BLOCK_JOB_COMPLETED" + } - { "timestamp": { "seconds": 1447193702, "microseconds": 632377 }, - "data": { "device": "drive1", "action": "report", - "operation": "read" }, - "event": "BLOCK_JOB_ERROR" } +#. Receive notification that the job for ``drive0`` has been cancelled: - .. code:: json + .. code:: json - { "timestamp": { "seconds": 1447193702, "microseconds": 640074 }, - "data": { "speed": 0, "offset": 0, "len": 67108864, - "error": "Input/output error", - "device": "drive1", "type": "backup" }, - "event": "BLOCK_JOB_COMPLETED" } + <- { + "timestamp": {...} + "data": { + "device": "drive0", + "type": "backup", + "speed": 0, + "len": 67108864, + "offset": 16777216 + }, + "event": "BLOCK_JOB_CANCELLED" + } - .. code:: json +At the conclusion of *this* example, both jobs have been aborted due to a +failure. Both destination images should be deleted and are no longer of use. - { "timestamp": { "seconds": 1447193702, "microseconds": 640163 }, - "data": { "device": "drive0", "type": "backup", "speed": 0, - "len": 67108864, "offset": 16777216 }, - "event": "BLOCK_JOB_CANCELLED" } +The transaction as a whole can simply be re-issued at a later time. .. raw:: html <!-- The FreeBSD Documentation License - Redistribution and use in source (Markdown) and 'compiled' forms (SGML, HTML, - PDF, PostScript, RTF and so forth) with or without modification, are permitted - provided that the following conditions are met: - - Redistributions of source code (Markdown) must retain the above copyright - notice, this list of conditions and the following disclaimer of this file - unmodified. - - Redistributions in compiled form (transformed to other DTDs, converted to PDF, - PostScript, RTF and other formats) must reproduce the above copyright notice, - this list of conditions and the following disclaimer in the documentation and/or - other materials provided with the distribution. - - THIS DOCUMENTATION IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" - AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE - IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE - DISCLAIMED. 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