Re: One Drive

Joe Jedynak wrote:
>
> We are new to ADSM. We have a 3570-Bll (one drive) tape subsystem (Magstar 
> MP).
> Now we have been told that to fully utilize ADSM we need to go to 3570-B12 
> (two drive) tape subsystem..
> Been trying to find info on this and have had no luck.

  Hi,

   Big reason for a multi-drive library: tape reclamation.

   After some period of time, any given tape will have some of
the data on it expire (extra versions that are abandoned,
versions that have reached their expiration time, etc.) When this
happens, ADSM will not try to reuse the portions of the tape where
the expired data lives, it will simply act as if that portion of
tape does not exist. If you have a multi-drive library, then ADSM
will, when the tape volume reaches it's % reclaimable limit,
migrate the remaining unexpired data from the tape in question to
a tape that is "filling" in that same library, and make the tape
in question's full capacity available to be used in the future.
If reclamation does not happen, then the tape volumes will be
left full of expired data, and unusable for storage of new data.

   In order to perform reclamation with a 1 drive library, you
must move the data from the tape in question to another storage
pool (can't be another library in the same storage pool!), then move
the data back so it lives in the right storage pool. This means you
must have another storage pool capable of temporarily housing the
unexpired data from the tape in question. It also means that you
must perform the move data interactively, where tape reclamation
happens automagically.

   This might not seem like a big deal for you now, but as your
installation ages and matures (and your library runs out of storage
capacity) it will become more important.

   Littler reason: speed. If you have a multidrive library, ADSM can
write to more than one drive simultaneously, speeding up the slowest
link in your ADSM chain. Things like library audits and libvol
checkins also get faster because multiple drives are involved.

   Hope this helps,

     Dan
--
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    is indistinguishable from magic.

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 Dan Jennings
 Assistant Information Systems Analyst
 CalTrans Engineering Service Center,
 Engineering Technology Support Branch,
 CADD Services Unit
 1801 30th St                  VOICE:          (916) 227-3970
 Sacramento, CA 95816          FAX:            (916) 227-8174
                               INTERNET:       tsdanj AT tsws.dot.ca DOT gov
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