Backup strategy for large mailbox stores

[Vincent Fox]

Forgot to mention we are running inline compression on
our ZFS pools.  With "fast" LZJB compression on the
filesystems for metadata etc. still a savings of ~2.0.
The inboxes are all in /var/cyrus/mail which is set for
gzip-6 compression savings of ~ 1.7.  Backups run
faster so it's win-win.

Combined with Cyrus single-instance store our I/O
channels are in fact fairly idle statistically 4% maybe
hitting 20% when busy.  The Sun V245 mail-stores
are fairly modest dual-CPU systems and load runs
~.7 most of the time so all this stuff which you would
assume would really shift a lot of load onto CPU doesn't
in fact result in any sort of bottleneck.