Adam,

This is only a guess, but maybe the move nodedata command is transferring
compressed data. If the data isn't being decompressed upon read and
re-compressed upon write then that would explain what appears to be lower
tape utilization. See what the query nodedata command shows before and
after the next move. Are you seeing an increase in the number of tapes
needed in the new pool compared to the old pool? It seems to me that if you
were losing compression then you would see at least a doubling of the
number of tapes being used in the new pool. If the number of tapes is about
the same then I wouldn't worry about it. If, on the other hand tape usage
is higher I'd give TSM support a call.

Rick Saylor

At 07:53 AM 2/22/2006, you wrote:

We have set up a new primary storage pool, using lto2 in a 3584 library,
with collocation by group. TSM5.3.2.1 on w2k3.
We are moving nodedata by collocation group from the original pool to the
new one in order to collocate our existing data.
In the original pool we see estimated tape capacities of up to 700GB. The
tapes being filled in the new pool are 280GB when 100% full.
Has anyone else experienced this apparent loss of compression when moving
data between pools, and what can we do to address it?

Adam Crosskey


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