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From: | John Snow |
Subject: | Re: [Qemu-devel] [Qemu-block] [RFC] Differential Backups |
Date: | Tue, 05 May 2015 11:55:49 -0400 |
User-agent: | Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.6.0 |
On 05/05/2015 06:25 AM, Stefan Hajnoczi wrote:
On Wed, Apr 29, 2015 at 06:51:08PM -0400, John Snow wrote:This is a feature that should be very easy to add on top of the existing incremental feature, since it's just a difference in how the bitmap is treated: Incremental - Links to the last incremental (managed by libvirt) - Clears the bitmap after creation Differential: - Links to the last full backup always (managed by libvirt) - Does not clear the bitmap after creation No biggie.Differential backups can be done using incremental backup functionality in QEMU: The client application points QEMU to the same target repeatedly instead of keeping separate incremental backups. Stefan
Oh, so you're saying: [anchor]<--[diff1]And then when making a new incremental, we re-use diff1 as a target and overwrite it so that it becomes:
[anchor]<--[diff2] In effect giving us a differential.OK, so it's possible, but we still lose out on some flexibility that a slightly different mode would provide us, like the ability to keep multiple differentials if desired. (Well, I suppose we *can* create those by manually copying differentials after we create them, but that seems hackier than necessary.)
Still, it would be such a paltry few lines of code and introduce no real complexity to the subsystem, and it might make libvirt's time a little easier for managing such things.
--js
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