Re: BTRFS as image store for KVM?

[Hugo Mills <hugo@carfax.org.uk>]

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On Thu, Sep 17, 2015 at 07:56:08PM +0200, Gert Menke 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.
> I'm honestly a bit confused here - isn't checksumming one of the
> most obvious things to want in a software RAID setup? Is it a
> feature that might appear in the future? Maybe I should talk to the
> md guys...
> 
> BTRFS looks really nice feature-wise, but is not (yet) optimized for
> my use-case I guess. Disabling COW would certainly help, but I don't
> want to lose the data checksums. Is nodatacowbutkeepdatachecksums a
> feature that might turn up in the future?
[snip]

   No. If you try doing that particular combination of features, you
end up with a filesystem that can be inconsistent: there's a race
condition between updating the data in a file and updating the csum
record for it, and the race can't be fixed.

   Hugo.

-- 
Hugo Mills             | I spent most of my money on drink, women and fast
hugo@... carfax.org.uk | cars. The rest I wasted.
http://carfax.org.uk/  |
PGP: E2AB1DE4          |                                            James Hunt

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