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?
Maybe ZFS is the best choice for my scenario. At least, it seems to work
fine for Joyent - their SmartOS virtualization OS is essentially Illumos
(Solaris) with ZFS, and KVM ported from Linux.
Since ZFS supports "Volumes" (virtual block devices inside a ZPool), I
suspect these are probably optimized to be used for VM images (i.e. do
as little COW as possible). Of course, snapshots will always degrade
performance to a degree.
However, there are some drawbacks to ZFS:
- It's less flexible, especially when it comes to reconfiguration of
disk arrays. Add or remove a disk to/from a RaidZ and rebalance, that
would be just awesome. It's possible in BTRFS, but not ZFS. :-(
- The not-so-good integration of the fs cache, at least on Linux. I
don't know if this is really an issue, though. Actually, I imagine it's
more of an issue for guest systems, because it probably breaks memory
ballooning. (?)
So it seems there are two options for me:
1. Go with ZFS for now, until BTRFS finds a better way to handle disk
images, or until md gets data checksums.
2. Buy a bunch of SSDs for VM disk images and use spinning disks for
data storage only. In that case, BTRFS should probably do fine.
Any comments on that? Am I missing something?
Thanks!
Gert
--
To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
