zfs discuss - Dec 2005 - Using zfs restore on a single-filesystem pool

I''ve been playing around with ZFS backup and restore, but I''ve
run into
an odd roadblock in that I can''t seem to restore a backup made from the
filesystem that gets created when you make a pool.  I can restore
backups from subordinate filesystems just fine, but I can''t figure out
how to restore the top-level filesystem.

For example, say I create a pool backed by a single 100MB file:

     # dd if=/dev/zero of=/tmp/pool-file bs=1048576 count=100
     # zpool create -m /tmp/mypool mypool /tmp/pool-file

Then, I put some files in that pool 

     # for I in 1 2 3 4 5
     > do 
     > dd if=/dev/zero of=/tmp/mypool/$I bs=1048576 count=5
     > done

I take a snapshot of the pool and then create a backup from that
snapshot:

     # zfs snapshot mypool at mysnapshot
     # zfs backup mypool at mysnapshot > /tmp/mysnapshot.backup

I now have a valid backup, but I can''t seem to restore it to its
original location.  If I try to restore it immediately, it fails because
the filesystem exists:

     # zfs restore mypool < /tmp/mysnapshot.backup
     cannot restore: destination fs mypool already exists

So I destroy the filesystem and try again (I have to use -r to get rid
of both the filesystem and its snapshot):

     # zfs destroy -r mypool
     # zfs restore mypool < /tmp/mysnapshot.backup
     cannot restore: destination fs mypool already exists

I suppose that this is an accurate error message because "zfs list"
still shows the mypool filesystem because it''s associated with the
mypool pool and you can''t have a pool without a filesystem (at least,
not after we got rid of containers).  But it looks like it''s preventing
me from being able to restore this backup.

I can create a new filesystem in the same pool from the backup, like:

     # zfs restore mypool/filesystem2 < /tmp/mysnapshot.backup

but that isn''t what I want because now my files are in
/tmp/mypool/filesystem2 rather than in /tmp/mypool like I want them to
be.  Is there any way to do this without using sub-filesytems?  And if
not, then can we have containers back so we can have a pool without a
filesystem?


Oh, and here''s what appears to be a bug in the restore process:  if you
destroy a pool, get rid of the backing file, remove the directory that
it was mounted in, and then try to restore a backup into its former
filesystem, then it will still say that the filesystem exists even when
there is no remnant of it left:

     # zfs destroy -r mypool
     # zpool destroy mypool
     # rm /tmp/pool-file
     # rmdir /tmp/mypool
     # zfs restore mypool < /tmp/mysnapshot.backup
     cannot restore: destination fs mypool already exists

The filesystem certainly does not exist because the pool that had
created it is gone along with the backing file and the mountpoint.


Neil

Yep, the inability to restore into the topmost filesystem is a known defeciency,
which we''re working on.

http://www.opensolaris.org/jive/message.jspa?messageID=16353#16353

Bug #6358519 ''zfs restore'' can''t restore full backup
into topmost filesystem
> # zfs restore mypool < /tmp/mysnapshot.backup
> cannot restore: destination fs mypool already exists
> 
> The filesystem certainly does not exist because the pool that had
> created it is gone along with the backing file and the mountpoint.
That looks like an incorrect error message to me, too.  Also, ''zfs
restore -r pool'' shouldn''t have appeared to work without
actually destroying the topmost filesystem.  I''ll get bugs filed on
these two...

Thanks for playing with backup/restore!

--matt
This message posted from opensolaris.org