a) Yes, we do backup with finer granularity.  However, if a RAID group fails, I have to restore the whole thing, so fine granularity does not help much :-(

b) Yes, I am thinking about switching to a 10 disk RAID group, with 2 per volume.  That makes for 3 shelves, 2 parity disks, and one hot spare.

c) We have a Gigabit network connection, so the 7MB/sec does seem slow.

-----Original Message-----
From: Louis Brune [mailto:lbrune@sd.us.am.ericsson.se]
Sent: Tuesday, September 19, 2000 10:47 AM
To: toasters@mathworks.com
Subject: Re: Optimal volume size

Fortunately for me, someone else here takes care of backups, but...

    We have a similar situation on our F740.  We want to keep the volume size
    small because:
    a) Restores can take forever as the data size gets bigger.

Can you not back up with qtree granularity instead of per volume?

    b) 10-14 disks is a good compromise on reliability.  Having 2 out of 14
    disks go bad at one time is much rarer than 2 out of 51 disks.

You can beat this by using several raid groups per volume.  Of course,
you need a parity drive for each raid group.

    c) If you upgrade disks/shelves in the future, you will likely do it a
    volume at a time. We did this with a volume with 180GB and the volcopy took
    6-7 hours to complete.  It is NOT very fast.  With 400GB+ in a volume, that
    should be 2-2.5x longer.

Hmm.  My data-shuffling tends to be in smaller pieces.  Wouldn't it be
nice to have a qtreecopy?  7 hours for 180 GB sounds like about 7
MB/second.  If this is on 100 MB, it's not all that bad.

--

                  Louis