I've been playing with btrfs as a backing store for my KVM images. I've used 'chattr +C' on the directory where those images are stored.
You can see my recipe below [1]. I've read the gotchas found here [2] I'm having continuing performance issues inside the Guest VM that is created inside the btrfs subvolume, using a qcow2 format. I'm having a hard time determining whether the issues are related to KVM or btrfs, or if this is even a reasonable topic of discussion. I've seen the comments on this list saying that if I want a COW filesystem with sparse files, that I'd be better off with ZFS. I'd like to use an in-tree COW filesystem, but if it's just not gonna happen yet with btrfs, I guess that's just the way it is. That being said, how would I determine what the root issue is? Specifically, the qcow2 file in question seems to have increasing fragmentation, even with the No_COW attr. [1] $ mkfs.btrfs -m raid10 -d raid10 /dev/sda /dev/sdb /dev/sdc /dev/sdd $ mount /dev/sda /mnt $ cd /mnt $ btrfs create subvolume __data $ btrfs create subvolume __data/libvirt $ cd / $ umount /mnt $ mount /dev/sda /var/lib/libvirt $ chattr +C /var/lib/libvirt/images $ cp /run/media/rbellamy/433acf1d-a1a4-4596-a6a7-005e643b24e0/libvirt/images/atlas.qcow2 /var/lib/libvirt/images/ $ filefrag /var/lib/libvirt/images/atlas.qcow2 /var/lib/libvirt/images/atlas.qcow2: 0 extents found [START UP THE VM - DO SOME THINGS] $ filefrag /var/lib/libvirt/images/atlas.qcow2 /var/lib/libvirt/images/atlas.qcow2: 12236 extents found [START UP THE VM - DO SOME THINGS] $ filefrag /var/lib/libvirt/images/atlas.qcow2 /var/lib/libvirt/images/atlas.qcow2: 34988 extents found [2] https://btrfs.wiki.kernel.org/index.php/Gotchas -- 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
