> Just a question about how to increase tape data copy speed. We are getting
> a tape copy speed of 15 gb/hr
> on stk-9840 drives with stk-9710 library. The tapes can run at a speed of
> 10 MB/sec which count to 36 GB/hr. We once when adsm-db is small, got a
> speed of tape copy in 23 minutes (20 gb). But now invariably
> we are getting a speed of 20gb in 1hr 20 minutes (fastest), that counts
> to about 15 gb/hr. (like move data,
> or migration or backup stg copies).
The TSM database is indeed in the midst of the activity, and so all the usual
database tuning factors (fast disk, memory caching, spreading over multiple
volumes for multi-threading, multiple processors, etc.) need to be taken into
account. The size of your aggregates, as governed by TXNGroupmax and
TXNBytelimit, affects the speed of operation across storage pools.
MOVEBatchsize will also affect throughput. TSM typically optimizes the
parameters for tape drives, though with 3rd party drives that becomes a gray
area. There is a limit to how much throughput you can expect as the intricacy
of operations increase as the volume of data increases in a system. Tape
storage pool backups will typically require more initial tape positioning
over time (mollified by serpentine tape track arrangements) to get to the
new data on the tape that needs to be backed up. Move Data operations
can be expected to involve considerable repositioning as the source tape is
processed, to skip over full-expired Aggregates. Migrations from a disk
storage pool with caching may involve numerous disk seeks to step to new,
unmigrated data, while the tape drive waits. Many factors come into play as
your system evolves.
I would assume that your four SCSI cards fast-wide-diff to make the most of
the drives. You might want to compare speeds when the copies happen to occur
across drives that are on separate SCSI chains vs. on a single chain, to see
if any significant difference which might argue for allocating just one
tape drive per SCSI adapter.
There is a document comparing 3590 vs. 9840 tape drives:
http://www.storage.ibm.com/hardsoft/tape/3590/prod_data/3590perform.pdf
It's not overly exciting, but provides some relative values.
Richard Sims, BU
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