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diff --git a/qemu/docs/bitmaps.md b/qemu/docs/bitmaps.md deleted file mode 100644 index a2e8d5116..000000000 --- a/qemu/docs/bitmaps.md +++ /dev/null @@ -1,505 +0,0 @@ -<!-- -Copyright 2015 John Snow <jsnow@redhat.com> and Red Hat, Inc. -All rights reserved. - -This file is licensed via The FreeBSD Documentation License, the full text of -which is included at the end of this document. ---> - -# 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 can be created at any time and attached to any node - (not just complete drives.) - -## Dirty Bitmap Names - -* A dirty bitmap's name is unique to the node, but bitmaps attached to different - nodes can share the same name. - -* Dirty bitmaps created for internal use by QEMU may be anonymous and have no - name, but any user-created bitmaps may not be. There can be any number of - anonymous bitmaps per node. - -* The name of a user-created bitmap must not be empty (""). - -## Bitmap Modes - -* 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. - -* The normal operating mode for a bitmap is "active." - -## Basic QMP Usage - -### Supported Commands ### - -* block-dirty-bitmap-add -* block-dirty-bitmap-remove -* block-dirty-bitmap-clear - -### Creation - -* To create a new bitmap, enabled, on the drive with id=drive0: - -```json -{ "execute": "block-dirty-bitmap-add", - "arguments": { - "node": "drive0", - "name": "bitmap0" - } -} -``` - -* 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. - -* To create a new bitmap that tracks changes in 32KiB segments: - -```json -{ "execute": "block-dirty-bitmap-add", - "arguments": { - "node": "drive0", - "name": "bitmap0", - "granularity": 32768 - } -} -``` - -### Deletion - -* Bitmaps that are frozen cannot be deleted. - -* 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. - -* Because bitmaps are only unique to the node to which they are attached, - you must specify the node/drive name here, too. - -```json -{ "execute": "block-dirty-bitmap-remove", - "arguments": { - "node": "drive0", - "name": "bitmap0" - } -} -``` - -### Resetting - -* Resetting a bitmap will clear all information it holds. - -* An incremental backup created from an empty bitmap will copy no data, - as if nothing has changed. - -```json -{ "execute": "block-dirty-bitmap-clear", - "arguments": { - "node": "drive0", - "name": "bitmap0" - } -} -``` - -## Transactions - -### 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: - -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. - -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. - -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: - -1. Boot the VM and begin execution. -2. 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. - -### Supported Bitmap Transactions - -* block-dirty-bitmap-add -* block-dirty-bitmap-clear - -The usages are identical to their respective QMP commands, but see below -for examples. - -### Example: New Incremental Backup - -As outlined in the justification, perhaps we want to create a new incremental -backup chain attached to a drive. - -```json -{ "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"} } - ] - } -} -``` - -### 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. - -```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. - -### 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. - - * Let's assume the full backup is named 'full_backup.img'. - * Let's assume the bitmap you created is 'bitmap0' attached to 'drive0'. - -2. Create a destination image for the incremental backup that utilizes the -full backup as a backing image. - - * Let's assume it is named 'incremental.0.img'. - - ```sh - # qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2 - ``` - -3. Issue the incremental backup command: - - ```json - { "execute": "drive-backup", - "arguments": { - "device": "drive0", - "bitmap": "bitmap0", - "target": "incremental.0.img", - "format": "qcow2", - "sync": "incremental", - "mode": "existing" - } - } - ``` - -### 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' - - ```sh - # qemu-img create -f qcow2 incremental.1.img -b incremental.0.img -F qcow2 - ``` - -2. Issue a new incremental backup command. The only difference here is that we - have changed the target image below. - - ```json - { "execute": "drive-backup", - "arguments": { - "device": "drive0", - "bitmap": "bitmap0", - "target": "incremental.1.img", - "format": "qcow2", - "sync": "incremental", - "mode": "existing" - } - } - ``` - -## Errors - -* 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. - -* 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 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. - -* 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. - -### Example - -1. Create a target image: - - ```sh - # qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2 - ``` - -2. Attempt to create an incremental backup via QMP: - - ```json - { "execute": "drive-backup", - "arguments": { - "device": "drive0", - "bitmap": "bitmap0", - "target": "incremental.0.img", - "format": "qcow2", - "sync": "incremental", - "mode": "existing" - } - } - ``` - -3. Receive an event notifying us of failure: - - ```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" } - ``` - -4. Delete the failed incremental, and re-create the image. - - ```sh - # rm incremental.0.img - # qemu-img create -f qcow2 incremental.0.img -b full_backup.img -F qcow2 - ``` - -5. Retry the command after fixing the underlying problem, - such as freeing up space on the backup volume: - - ```json - { "execute": "drive-backup", - "arguments": { - "device": "drive0", - "bitmap": "bitmap0", - "target": "incremental.0.img", - "format": "qcow2", - "sync": "incremental", - "mode": "existing" - } - } - ``` - -6. Receive confirmation that the job completed successfully: - - ```json - { "timestamp": { "seconds": 1424709668, "microseconds": 526525 }, - "data": { "device": "drive1", "type": "backup", - "speed": 0, "len": 67108864, "offset": 67108864}, - "event": "BLOCK_JOB_COMPLETED" } - ``` - -### 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. - -* 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. - -* 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. - -#### Example - -* QMP example highlighting two backup jobs: - - ```json - { "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" } }, - ] - } - } - ``` - -* QMP example response, highlighting one success and one failure: - * Acknowledgement that the Transaction was accepted and jobs were launched: - ```json - { "return": {} } - ``` - - * Later, QEMU sends notice that the first job was completed: - ```json - { "timestamp": { "seconds": 1447192343, "microseconds": 615698 }, - "data": { "device": "drive0", "type": "backup", - "speed": 0, "len": 67108864, "offset": 67108864 }, - "event": "BLOCK_JOB_COMPLETED" - } - ``` - - * Later yet, QEMU sends notice that the second job has failed: - ```json - { "timestamp": { "seconds": 1447192399, "microseconds": 683015 }, - "data": { "device": "drive1", "action": "report", - "operation": "read" }, - "event": "BLOCK_JOB_ERROR" } - ``` - - ```json - { "timestamp": { "seconds": 1447192399, "microseconds": 685853 }, - "data": { "speed": 0, "offset": 0, "len": 67108864, - "error": "Input/output error", - "device": "drive1", "type": "backup" }, - "event": "BLOCK_JOB_COMPLETED" } - -* 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." - -### Grouped Completion Mode - -* 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. - -* QMP transactions take an optional properties structure that can affect - the semantics of the transaction. - -* The "completion-mode" transaction property can be either "individual" - which is the default, legacy behavior described above, or "grouped," - a new behavior detailed below. - -* Delayed Completion: In grouped completion mode, no jobs will report - success until all jobs are ready to report success. - -* 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. - - * Regardless of if QEMU reports a particular incremental backup job as - CANCELLED or as an ERROR, the in-memory bitmap will be restored. - -#### Example - -* Here's the same example scenario from above with the new property: - - ```json - { "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" - } - } - } - ``` - -* QMP example response, highlighting a failure for drive2: - * Acknowledgement that the Transaction was accepted and jobs were launched: - ```json - { "return": {} } - ``` - - * Later, QEMU sends notice that the second job has errored out, - but that the first job was also cancelled: - ```json - { "timestamp": { "seconds": 1447193702, "microseconds": 632377 }, - "data": { "device": "drive1", "action": "report", - "operation": "read" }, - "event": "BLOCK_JOB_ERROR" } - ``` - - ```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" } - ``` - - ```json - { "timestamp": { "seconds": 1447193702, "microseconds": 640163 }, - "data": { "device": "drive0", "type": "backup", "speed": 0, - "len": 67108864, "offset": 16777216 }, - "event": "BLOCK_JOB_CANCELLED" } - ``` - -<!-- -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. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE -FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL -DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR -SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER -CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, -OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF -THIS DOCUMENTATION, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. ---> |