It seems reasonable. You probably don't have to use the mirroring
feature to backup the backup since they are local disks but it is
fun to play with.
If you use mirror-stream instead of mirror-copy you can control the
bandwidth used by the mirroring operation (so as not to interfere with
other things happening on the machine) and it will run continuously.
So for example this will limit the mirroring bandwidth to 5 MBytes/sec:
hammer -b5m mirror-stream masterpfs slavepfs
mirror-stream only exits if the connection is lost so it is still a
good idea to check-start it with cron. I usually use lockf for that
and a simple script. Also make sure it isn't being verbose when run
from cron or poor cron will be collecting a very large temporary mail
file.
10 1 * * * (cd ~/adm; /usr/bin/lockf -k -t 0 .lockmirror ./do_mirror 1)
:#hammer pfs-slave /Backup2/Data
shared-uuid=7f37a084-6188-11de-958a-535400123456
:#hammer pfs-status /Backup2/Data
On the PFS's, the convention is to create them in <basefs>/pfs/NAME and
then use null mounts to put them where you actually want them. e.g.:
hammer pfs-slave /Backup2/pfs/Data
mkdir /Backup2/Data
mount_null /Backup2/pfs/Data /Backup2/Data
In /etc/fstab a null mount looks something like this:
# Device Mountpoint FStype Options Dump Pass#
/pfs/home /home null rw 0 0
/pfs/usr.obj /usr/obj null rw 0 0
null mounts aren't quite as useful for PFS slaves since a null mount
will lock-in the slave TID instead of tracking it. In that case a
second softlink might be reasonable instead of using a NULL mount.
In anycase, if redundancy is that important to you for the backup box
then I recommend a combination of a SATA SSD (SATA-based solid state
flash drive) and two hard drives. Put the main system on the SSD and
only use the hard drives for the two HAMMER filesystems.
If the motherboard supports AHCI you probably also want to use the
AHCI disk driver, which is new in the master branch. The NATA driver
cannot do NCQ. The drives will be recognized as da0, da1, da2, etc...
instead of adX. Also, the AHCI driver can handle hot-plug (though you
still need to be sure to umount the filesystem(s) before removing the
HD). In that case the SSD would be the machine's internal drive and
you would use hot-plug hard disks as two external ESATA drives in an
enclosure, or something on that order.
-Matt
Matthew Dillon
<dil...@backplane.com>
