ADSM-L

Consolidation of Off-site tapes

1997-05-23 13:50:38
Subject: Consolidation of Off-site tapes
From: Peter Talajic <pmt2f AT UOTTAWA DOT CA>
Date: Fri, 23 May 1997 13:50:38 -0400
I have a question concerning the consolidation of off-site tapes:  Is there
a better way??  Let me explain.

In order to recover from a complete disaster at the main computer
site, copies of all data in the primary storage pools is made to
tape, and these tapes are taken to an off-site storage location.  The
primary pools are located on both disk and tape (six on disk, six on
tape, and one of the tape pools is collocated).  The copies are made
each day, so each off-site tape contains a mix of data from multiple
primary pools.

As time goes by, expire processes delete files, and the percentage
of valid data on those off-site tapes decreases.  Eventually, it is
necessary to consolidate that data in order to recover some tapes.
Since all the off-site information still exists in the primary pools,
a MOVE DATA command can be issued against the off-site tape, and
local tapes will be read to accomplish the move operation.

Now the problem:  moving the first off-site tape will cause several
local tapes to be mounted.  Once that is complete, a move command is
issued for the second off-site tape.  This causes many of the same
local tapes to be mounted again.

In our case, the tapes being used are 8mm, which take a very long
time to skip from one file to the next.  Since only a few files are
being read from each local tape on any given pass, the process can
take several hours to move a relatively small amount of data.

Is there any way to tell ADSM that several off-site tapes are to be
processed in one pass, thus causing the local tapes to be mounted
only once?

Looking in the manual I see the RESTORE VOLUME command which does a
single pass for multiple volumes, but the RESTORE command reads
copypool tapes to rebuild a primarypool volume, while we want to read
primarypool tapes to rebuild copypool volumes.

One solution we've come up with is to wait until the percentage of valid
data on the off-site tape becomes VERY LOW.  Then, the number of input tapes
mounted during a consolidate is minimized.  Unfortunately, this also means
that the number of off-site tapes increases!  We don't like the idea of
having over three times as many off-site tapes as primary tapes.

Other suggestions?

Peter.
<Prev in Thread] Current Thread [Next in Thread>