James... this is thorny issue considering the cost of these tapes. I use Magstar
MP C-Format XL tapes and these guys
cost about $75 a pop. Be conservative when ordering and get more than you think
you will need. I have experimented with
client compression vs drive compression and since I have a solid ETHERNET
infrastructure, chose to rely on drive
compression. Having said that, I snipped a portion of the result of a 'q vol'
listing:

00E195                       ARTPOOL2        3575DEVC1            6,340.1
56.9       Full
00E1A6                       BKTPOOL2        3575DEVC1            6,809.4
84.6       Full
00E1AA                       ARTPOOL1        3575DEVC1            20,369.6
74.2       Full
00E1F2                       BKTPOOL1        3575DEVC1            9,238.7
50.5       Full
00E208                       BKTPOOL1        3575DEVC1            31,779.1
100.0       Full
00E20F                       ARTPOOL2        3575DEVC1            9,901.6
62.2       Full

Note that the estimated capacity of the 7 volumes varies wildly from a low of
about 8 gigs to over 31 gigs... It all depends on
what type data you back up. Don't feel that any simple form would prove of much
value unless it was able to compensate for
the effect of compression on different types of data or you could find a site
where the data types were similar to yours, have
them multiply the estimated volume capacity for the separate volumes and then
divide by the sum of the volumes to give you
a gestimate number on the amount you could expect per volume... Other factors
are finding an average amount of data backed
up... once on a production basis with TSM, you could check the amount moved
during the backup of the primary tape storage
pool to the copy pool to get this number. Since I took this job over and have
sorted out most of our requirements and schedules,
we have gone from about 30 gigs per day (during the week-only backups are
included in this number) to about 100 gigs per
day.  I guess what I am suggesting is to buy a supply of tapes, make the people
with the money aware that you have not
established a baseline for the tape purchase and then work with the limited
supply of tapes for a few months to develop this
baseline and then purchase what you really require plus some percentage for
growth... Hope this helps... this is how I would
have done this, if I had known what I know now ;-)

George Lesho
Storage/System Admin
AFC Enterprises





"<James> <healy>" <James.Healy2 AT AXACS DOT COM> on 02/15/2001 02:34:02 PM

Please respond to "ADSM: Dist Stor Manager" <ADSM-L AT VM.MARIST DOT EDU>

To:   ADSM-L AT VM.MARIST DOT EDU
cc:    (bcc: George Lesho/Partners/AFC)
Fax to:
Subject:  Formula to calculate # tapes required



Does  any one out there have a formula they use to calculate the number of
tapes they will use for an instance of TSM
I've tried to start with
          1) size of file systems to backup x 1 because you have at least 1
backup version of every file on the systems you'll back up(roughly)
          2) estimate the percentage of data that changes in you
environment daily, multiply that by the number of versions you'll keep
          add numbers 1 and two together to get a number that equals the
amount of data you'll have in your backup system onsite.
     here's where it gets fuzzy. Somehow you have to calculate the amount
of data you'll have co-located and non colocated. Find an average of the
capacity  your getting on your tapes. Then you'll have a number of what
your on-site capacity should be. Now you can double that if you're using
DRM and then somehow calculate in the factor of the re-use delay parameter
for the storage pools?????????????????