Victor Zhang wrote:
Hello list,
I have a dumb question regarding logical volumes written to IBM's VTS,
is
the data compressed or not?
IBM recently announced next generation of VTS:TS7700, from its
production
description, only usable capacity(raw disk capactiy - meta data
overhead).When it is talking about backend tape drives, it only mentions
that TS1120 or 3592 can compress data at a ratio of about 3:1.
That raises my confustion: is data written to VTS cache compressed or
not?
It depends. Older VTSes (B16) didn't have such option. Later it was an
optional feature - EHPO (Extended High Performance Option). With EHPO,
data is compressed when coming from host. Usable cache capacity grew up
with that. What's interesting, the compressed data is destaged on real
(stacked) tape volumes with "drive compression" turned on, but obviously
it doesn't provide better compression.
--
Radoslaw Skorupka
Lodz, Poland
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