Abi said, in part..
> Following in the formula given in the Administrator's Guide, I calculated
> the space needed for BACKUPPOOL:
>
> backupspace = AvgWkstSize * utilization * VersionExpansion * NumWkst
> = 325MB * .70 * 1.05 * 122
> = 29,142.75 MB
> Is this number including data that is migrating to tapes?
>
> How can I find out what the optimum size for our disk storage pool is?
That calculation is for *total* space for all files. So you need that
much disk space only if you want everything on the disk. If you
really want a disk pool just for performance of the backup and to hold
some changed files for expected restore, then you need much less disk.
IMHO, you need enough disk to hold at least one day's backup. The more
days backups it will hold, the better, as more files are available for
restore and, since migration to the disk pool is by client, the fewer
tapes might be needed to restore any one client. When estimating "one
day's backup", remember that a few people will probably be starting to
use ADSM backup on some file system now and again .. maybe every day
with your over 100 clients.
IMHO, the above calculation leads to a grossly understated tape volume
requirement. It may be an OK estimate of the amount of data, for now,
but your tapes cannot be all full .. or if they are, your tape operators
are going to be very busy. Much better to have twice that many tapes
(for example), or more, so tape to tape migrations may be delayed
until a tape is relatively empty (say 40%).
Obviously, a couple of the numbers above will vary over time. Average
disk space per user might be expected to increase as disk gets cheaper
and applications want more, lots more in the case of multi-media.
Also, note that ADSM backs up by file system (or volume label in the
case of Windows). If someone relabels a disk volume, then ADSM will
leave the old backed up volume files (forever) and completely backup
the "new volume". I have some users that will delete these old
backups, but most will not. The 1.05 factor for changed files must be
adjusted upwards by some amount to take this into account.
Your backup policies will have an effect on the storage required. The
more "inactive" copies allowed and the longer they are kept, the more
space you will need. Also in this policy category are be the effects of
"point-in-time-restore", should ADSM ever support it.
Finally, you will probably have some clients that don't fit into your
average. For example, I have a few clients that have several
gigabytes of data and change one gig each day. Perhaps it is needless
to say that these clients don't look anything like the typical Mac and
Windows client that changes a half-dozen small files each day?
Hope this helps,
Wayne T. Smith
Systems Group -- CAPS internet: wts AT maine.maine DOT edu
University of Maine System BITNET/CREN: WTS@MAINE
|
