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Re: [Qemu-devel] [RFC 4/8] block: add block_backup QMP command
From: |
Eric Blake |
Subject: |
Re: [Qemu-devel] [RFC 4/8] block: add block_backup QMP command |
Date: |
Thu, 14 Mar 2013 15:52:16 -0600 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130219 Thunderbird/17.0.3 |
On 03/09/2013 03:22 PM, Stefan Hajnoczi wrote:
> @block-backup
>
> Start a point-in-time copy of a block device to a new destination.
>
I'm trying to figure out how this is different from drive-mirror. If I
understand correctly:
After starting drive-mirror, a write to the block device is also written
to the mirror, so that the destination sees the new data
After starting block-backup, a write to the block device flushes the old
data to the destination, so that the destination sees the old data
Timing-wise, I can accomplish a backup through either command, with the
following differences:
With drive-mirror, I start a job, wait for it to hit sync'd state, then
cancel the job. The copy is tied to the point where I cancel, and the
moment I cancel, I no longer have to worry about keeping the destination
writable (that is, the bulk of the copying is done prior to the point in
time).
With block-backup, I start a job, then wait for it to complete. The
copy is tied to the point where I started the job, but as that may take
some time, I have to keep the destination writable until the job
completes (that is, the bulk of the work is done after the point in time).
The concept is indeed useful; more so if we can wire this into
'transaction' to capture multiple disks at the same point in time.
--
Eric Blake eblake redhat com +1-919-301-3266
Libvirt virtualization library http://libvirt.org
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- [Qemu-devel] [RFC 0/8] block: Live backup prototype, Stefan Hajnoczi, 2013/03/09
- [Qemu-devel] [RFC 1/8] block: add virtual_size to query-block QMP output, Stefan Hajnoczi, 2013/03/09
- [Qemu-devel] [RFC 2/8] add basic backup support to block driver, Stefan Hajnoczi, 2013/03/09
- [Qemu-devel] [RFC 4/8] block: add block_backup QMP command, Stefan Hajnoczi, 2013/03/09
- [Qemu-devel] [RFC 5/8] Add nbd server Python module, Stefan Hajnoczi, 2013/03/09
- [Qemu-devel] [RFC 6/8] Add VMA backup archive writer Python module, Stefan Hajnoczi, 2013/03/09
- [Qemu-devel] [RFC 7/8] Add vma-writer.py tool, Stefan Hajnoczi, 2013/03/09
- [Qemu-devel] [RFC 8/8] Add backup.py tool, Stefan Hajnoczi, 2013/03/09
- [Qemu-devel] [RFC 3/8] backup: write to BlockDriverState instead of BackupDumpFunc, Stefan Hajnoczi, 2013/03/09
- Re: [Qemu-devel] [RFC 0/8] block: Live backup prototype, Dietmar Maurer, 2013/03/10