Andy Raibeck posted the following:

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My own opinion on this: disk space costs some amount of dollars, and so it
makes sense to try to utilize it as effectively as possible. Especially in the
case of disk backup storage pools, you're only putting backup versions out
there. This means that the odds of you ever reading that data back are slim to
none. When I was at Connecticut Mutual, I set up the disk backup pool so that it
would be of sufficient size ot house one night's worth of data. During the day,
I would migrate most of the data to tape. Thus in addition to the slim
likelihood of the data ever being read back, it doesn't make sense to cache the
disk backup pool.
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Andy -

Perhaps this is the proverbial "Glass half full" issue.  I agree with your
statements about costs of DASD, and trying to keep the disk pool at a size that
holds one day's worth of backups.  We use the same guidelines.  However, I use
caching, and think it valuable.  My logic goes along the following lines -
basically - I need to have "X" amount of pool space available to handle the
day's activities; when I reach my thresholds (or I force it), the migration
happens.  Until this happens again, the data is available in two places - on
tape and in the pool.  There is no guarantee that the data will be in the pool -
it is in essence a "Freebie".  And if in the event that someone needs a restore
and it resides in the cache - so much the better - the customer gets better
response, and we have one less tape mount to worry about - even if it is
automated.  I don't maintain extra capacity to handle a cache, so why not use it
to provide better service if possible?

Jerry

Jerry Lawson
ITT Hartford Insurance Group
jlawson AT itthartford DOT com
(203) 547-2960