raw fs backup/copy
Is there a reason one can not mount a btrfs and it's byte-for-byte copy in parallel, or is the driver just acting silly?
Mini example:
# dd if=/dev/zero of=fs1 bs=1 count=1 seek=$((1024*1024*1024-1)) # mkfs.btrfs fs1 # cp --sparse=always fs1 fs2 # mkdir 1 2 # mount fs1 1 -o loop # mount fs2 2 -o loop # touch 1/1 # ls 2 1 # cat /proc/mounts /dev/loop0 /tmp/test/1 btrfs rw,relatime 0 0 /dev/loop1 /tmp/test/2 btrfs rw,relatime 0 0
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ivan
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Quoted 5 lines · Hugo Mills
Quoted 2 lines · On Thu, Jan 06, 2011 at 05:36:48PM +0100, Ivan Lab=C3=A1th wrote:
Is there a reason one can not mount a btrfs and it's byte-for-byte copy in parallel, or is the driver just acting silly?
=20
Probably because both filesystems have identical UUIDs (and labels=
)
Quoted 1 line
and so will (I suspect) end up being identified as the same filesyste=
m
Quoted 4 lines
by the btrfs code.
=20
Hugo.
=20
The reason I ask is, that I had a mirror RAID (btrfs on LVM on LUKS on = RAID)
across 2 disks. Then I snatched one to take with me when going away for holidays, copied some files on to it and when I came back, I wanted to = get
to those files. The problem was, I couldn't mount the fs I took with me= ,
because a similar fs was already mounted. As it wasn't the root fs, I could unmount it and copy the files on some other fs (though one could use pivot_root, if it was the root fs).
It seems to me there are cases, where one would want to mount two copie= s of
originally the same filesystem - think of RAID, VMs, distributing fs im= ages
on a network, LVM snapshots, backups, etc.
--
ivan
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