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Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command
From: |
Wenchao Xia |
Subject: |
Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command |
Date: |
Thu, 16 May 2013 14:16:20 +0800 |
User-agent: |
Mozilla/5.0 (Windows NT 5.1; rv:17.0) Gecko/20130328 Thunderbird/17.0.5 |
δΊ 2013-5-15 22:34, Stefan Hajnoczi ει:
> Note: These patches apply to my block-next tree. You can also grab the code
> from git here:
> git://github.com/stefanha/qemu.git block-backup-core
>
> This series adds a new QMP command, drive-backup, which takes a point-in-time
> snapshot of a block device. The snapshot is copied out to a target block
> device. A simple example is:
>
> drive-backup device=virtio0 format=qcow2 target=backup-20130401.qcow2
>
> The original drive-backup blockjob was written by Dietmar Maurer
> <address@hidden>. He is currently busy but I feel the feature is worth
> pushing into QEMU since there has been interest. This is my version of his
> patch, plus the QMP command and qemu-iotests test case.
>
> QMP 'transaction' support is included since v3. It adds support for atomic
> snapshots of multiple block devices. I also added an 'abort' transaction to
> allow testing of the .abort()/.cleanup() code path. Thanks to Wenchao for
> making qmp_transaction() extensible.
>
> How is this different from block-stream and drive-mirror?
> ---------------------------------------------------------
> Both block-stream and drive-mirror do not provide immediate point-in-time
> snapshots. Instead they copy data into a new file and then switch to it. In
> other words, the point at which the "snapshot" is taken cannot be controlled
> directly.
>
> drive-backup intercepts guest writes and saves data into the target block
> device before it is overwritten. The target block device can be a raw image
> file, backing files are not used to implement this feature.
>
> How can drive-backup be used?
> -----------------------------
> The simplest use-case is to copy a point-in-time snapshot to a local file.
>
> More advanced users may wish to make the target an NBD URL. The NBD server
> listening on the other side can process the backup writes any way it wishes.
> I
> previously posted an RFC series with a backup server that streamed Dietmar's
> VMA backup archive format.
>
> What's next for drive-backup?
> -----------------------------
> 1. Sync modes like drive-mirror (top, full, none). This makes it possible to
> preserve the backing file chain.
>
> v3:
> * Rename to drive-backup for consistency with drive-mirror [kwolf]
> * Add QMP transaction support [kwolf]
> * Introduce bdrv_add_before_write_cb() to hook writes
> * Mention 'query-block-jobs' lists job of type 'backup' [eblake]
> * Rename rwlock to flush_rwlock [kwolf]
> * Fix space in block/backup.c comment [kwolf]
>
> v2:
> * s/block_backup/block-backup/ in commit message [eblake]
> * Avoid funny spacing in QMP docs [eblake]
> * Document query-block-jobs and block-job-cancel usage [eblake]
After checking the code, I found it possible to add delta data backup
support also, If an additional dirty bitmap was added. Compared with
current solution, I think it is doing COW at qemu device level:
qemu device
|
general block layer
|
virtual format layer
|
-----------------------
| |
qcow2 vmdk....
This will make things complicated when more works comes, a better
place for block COW, is under general block layer. Maybe later we
can adjust block for it.
--
Best Regards
Wenchao Xia
- Re: [Qemu-devel] [PATCH v3 3/8] block: add drive-backup QMP command, (continued)
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Paolo Bonzini, 2013/05/17
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Stefan Hajnoczi, 2013/05/20
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Paolo Bonzini, 2013/05/20
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Stefan Hajnoczi, 2013/05/21
- Re: [Qemu-devel] [PATCH v3 0/8] block: drive-backup live backup command, Paolo Bonzini, 2013/05/21