ZFS backups: retrieving a few files?

Andrew Reilly areilly at bigpond.net.au
Mon Nov 22 11:35:55 UTC 2010

Hi there,

Being a cutting-edge hipster, my new personal server is using a
ZFS RAIDZ array, where my older system used UFS on a GMIRROR.
This is, by and large, a joy: ZFS rocks.

One issue that I'm having difficulty coming to grips with,
though, is that of backup.  I used to do a weekly cycle (with a
two week retention) of incremental backups to an external hard
drive.  Dump/restore allowed this to be useful both for disaster
(hardware failure) recovery and for clumsiness (file destruction)

Dump/restore doesn't work for ZFS.  I *think* that I'm running
backups in the appropriate equivalent fashion: I take file
system snapshots (both absolute == level 0) and relative
(incremental), and zfs send those to files on the backup disk.
I haven't tried the recovery procedure yet, but it seems that
one would zfs receive the same files to snapshots, and then
either grab the files scrunged or perform the snapshot->working
file system upgrade process described in the manual, depending
on the situation.

The troubling aspect of this plan is that it would seem that
grabbing just a few files would require space in the working
zpool equivalent to the whole backed-up file system, for the
zfs receive of the snapshot.  Contrast this with restore, which
had a nice interactive (or command line) mode of operation that
could retrieve nominated files or directories, requiring only
space for the results.  Is there any similar tool that can
operate on a ZFS "send" serialization?  It would seem that the
information must be "in" there somewhere, but I've not heard of

Clues?  How does everyone else manage this?



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