Backing up ZFS to an external USB drive

Having a resilient, snapshot managed storage server is all very well, but what happens if your server catches fire? While ZFS is very capable of preventing data loss, and the RAID capabilities compensate for a physical disk failure, the lack of a ufsdump/ufsrestore was a bit troubling.

I'm not claiming to have found the perfect solution, but a bit of playing around today with an external USB disk looks promising. I plugged the USB drive in and OpenSolaris automatically detected it. Running the format command showed it was mapped to c6t0d0.

I partitioned the disk to create a single 500GB(ish) slice 0 and created a traditional UFS filesystem on it. I'm sure I could have used ZFS, but wanted the simplicity of a single filesystem without worrying about pools or other volume manager artifacts.

After creating the filesystem with newfs, I mounted it to /mnt.

# newfs -m5 /dev/rdsk/c6t0d0s0
# mount /dev/dsk/c6t0d0s0 /mnt

I had a test filesystem created (datapool/testfs) and copied a file into it. I then took a snapshot of the filesystem:

# zfs snapshot datapool/testfs@mytest

I backed up the snapshot using the ZFS send syntax:

# zfs send datapool/testfs@mytest > /mnt/testfs.backup

This created a single file (/mnt/testfs.backup) containing the filesystem.

With that completed, I deleted the file I copied across. Now for the restore. This was very easy:

# zfs recv datapool/testfs.recover < /mnt/testfs.backup

A new filesystem was created and mounted in /datapool/testfs.recover, containing the file I wanted to recover which I could then copy back. To test a bit further, I destroyed the original datapool/testfs filesystem and all snapshots. I then did another zfs recv and specified the original filesystem name:

# zfs recv datapool/testfs < /mnt/testfs.backup

And it all came back perfectly!

Obviously this is a simple test and doesn't deal with incrementals etc, but should be sufficient for a keeping a copy of the data on an external disk that can be stored off site. Although I haven't tried, adding encryption to the zfs send pipeline should be very simple to do.

ZFS just gets better and better!