On 11/21/2014 05:28 AM, Zygo Blaxell wrote: > e.g. if an ext4 filesystem explodes, I can: > > 1. make a LVM snapshot of the broken filesystem > > 2. run e2fsck on the snapshot > > 3. mount and repair the snapshot, e.g. rsync any missing files > from backups, salvage anything that survived > > 4. LVM merge the snapshot to its origin volume > > 5. umount the origin volume and mount the merged volume > (or just reboot) > > ...and I can do all of this on a running system, in-place, with only a > few minutes of downtime in the must-reboot case. > > None of the above works with btrfs at all. Multi-device btrfs fails > at 2,
You can't compare ext4 with btrfs, if you are talking about a multi-device filesystem: ext4 haven't this capability. Try to make a md-raid over a snapshotted logical volume(s); I never tried that, but I suppose that there will be the same problems... > and mounting the filesystem fails at 3. Are you sure ? ghigo@venice:/tmp$ # create a btrfs filesystem in a logical volume ghigo@venice:/tmp$ sudo truncate -s +10G disk.img ghigo@venice:/tmp$ sudo losetup -f disk.img ghigo@venice:/tmp$ sudo pvcreate /dev/loop0 ghigo@venice:/tmp$ sudo vgcreate vgtest /dev/loop0 ghigo@venice:/tmp$ sudo lvcreate -n lvone -L 3G vgtest ghigo@venice:/tmp$ sudo mkfs.btrfs /dev/vgtest/lvone ghigo@venice:/tmp$ mkdir t ghigo@venice:/tmp$ # create a file inside a btrfs fs ghigo@venice:/tmp$ sudo mount /dev/vgtest/lvone t/ ghigo@venice:/tmp$ sudo dd if=/dev/zero of=t/disk-orig bs=1M count=1 ghigo@venice:/tmp$ sudo umount t ghigo@venice:/tmp$ # make a lvm snapshot and add a 2nd file ghigo@venice:/tmp$ sudo lvcreate -s -n lvone_snap -L 3G vgtest/lvone ghigo@venice:/tmp$ sudo mount /dev/vgtest/lvone_snap t/ ghigo@venice:/tmp$ sudo dd if=/dev/zero of=t/disk-snap bs=1M count=1 ghigo@venice:/tmp$ sudo umount t ghigo@venice:/tmp$ # mount the first one lv, and check the file ghigo@venice:/tmp$ sudo mount /dev/vgtest/lvone t/ ghigo@venice:/tmp$ ls -l t total 1024 -rw-r--r-- 1 root root 1048576 Nov 22 18:11 disk-orig ghigo@venice:/tmp$ sudo umount t ghigo@venice:/tmp$ # mount the first one lv, and check the files ghigo@venice:/tmp$ sudo mount /dev/vgtest/lvone_snap t/ ghigo@venice:/tmp$ ls -l t total 2048 -rw-r--r-- 1 root root 1048576 Nov 22 18:11 disk-orig -rw-r--r-- 1 root root 1048576 Nov 22 18:12 disk-snap On the basis of the example above, in case you want to mount a "single-disk", BTRFS seems me to work properly. You have to pay attention only to not mount the two filesystem at the same time. BR G.Baroncelli -- gpg @keyserver.linux.it: Goffredo Baroncelli <kreijackATinwind.it> Key fingerprint BBF5 1610 0B64 DAC6 5F7D 17B2 0EDA 9B37 8B82 E0B5 -- 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
