Re: BTRFS as image store for KVM?

[Austin S Hemmelgarn <ahferroin7@gmail.com>]

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On 2015-09-17 14:35, Chris Murphy wrote:
> On Thu, Sep 17, 2015 at 11:56 AM, Gert Menke <gert@menke.ac> wrote:
>> Hi,
>>
>> thank you for your answers!
>>
>> So it seems there are several suboptimal alternatives here...
>>
>> MD+LVM is very close to what I want, but md has no way to cope with silent
>> data corruption. So if I'd want to use a guest filesystem that has no
>> checksums either, I'm out of luck.
>
> You can use Btrfs in the guest to get at least notification of SDC. If
> you want recovery also then that's a bit more challenging. The way
> this has been done up until ZFS and Btrfs is T10 DIF (PI). There are
> already checksums on the drive, but this adds more checksums that can
> be confirmed through the entire storage stack, not just internal to
> the drive hardware.
>
> Another way is to put a conventional fs image on e.g. GlusterFS with
> checksumming enabled (and at least distributed+replicated filtering).
>
> If you do this directly on Btrfs, maybe you can mitigate some of the
> fragmentation issues with bcache or dmcache; and for persistent
> snapshotting, use qcow2 to do it instead of Btrfs. You'd use Btrfs
> snapshots to create a subvolume for doing backups of the images, and
> then get rid of the Btrfs snapshot.
>
>
The other option (which for some reason I almost never see anyone 
suggest), is to expose 2 disks to the guest (ideally stored on different 
filesystems), and do BTRFS raid1 on top of that.  In general, this is 
what I do (except I use LVM for the storage back-end instead of a 
filesystem) when I have data integrity requirements in the guest.  On 
the other hand of course, most of my VM's are trivial for me to 
recreate, so I don't often need this and just use DM-RAID via LVm.


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