[CentOS] Looking for a life-save LVM Guru

And then Btrfs (no LVM).
mkfs.btrfs -d single /dev/sd[bcde]
mount /dev/sdb /mnt/bigbtr
cp -a /usr /mnt/bigbtr

Unmount. Poweroff. Kill 3rd of 4 drives. Poweron.

mount -o degraded,ro /dev/sdb /mnt/bigbtr   ## degraded,ro is required
or mount fails
cp -a /mnt/bigbtr/usr/ /mnt/btrfs    ## copy to a different volume

No dmesg errors. Bunch of I/O errors only when it was trying to copy
data on the 3rd drive. But it continues.

# du -sh /mnt/btrfs/usr
2.5G usr

Exactly 1GB was on the missing drive. So I recovered everything that
wasn't on that drive.

One gotcha that applies to all three fs's that I'm not testing: in-use
drive failure. I'm simulate drive failure by first cleanly unmounting
and powering off. Super ideal. How the file system and anything
underneath it (LVM and maybe RAID) handles drive failures while in
use, is a huge factor.


Chris Murphy