On 01/23/2012 10:09 AM, Staller, Allan wrote:
Generally speaking...Yes
<snip>
IOW, the response time is more likely to increase than to decrease,
and increased response time is a Bad Thing
</snip>
PAV, Cache, and RAID all have impacts that mitigate the 1:3 (or worse)
actuator to data ratio on mod 9 vs. 3 mod 3.
These impacts may not be part of the intended design.
As with most things, YMMV. Few large datasets are less impacted than
many small datasets.
...
With PAV, if you use PAVs to give the same total number of addresses to
the mod 9 as were previously on the three mod-3's it replaces, you could
conceivably even get better response from lower IOSQ time from the
merging of available PAVs of three volumes into a single pool (unless
you are already getting this benefit from Hiper-PAV support)
Without appropriately configured PAV, the result is an unknown.
Depending on how heavy the concurrent loading of the original mod-3's,
you could have anywhere from severe IOSQ delays and response problems to
inconsequential IOSQ delays and minimal increase in response time.
While it may be easier to conceive of many concurrent users on a volume
with many small datasets, large multi-volume sequential datasets can
easily have high concurrent usage on different volumes from readers in
multiple critical batch workloads; and large VSAM datasets, as in this
case, could easily have a large amount of concurrent access on multiple
volumes from concurrent on-line transactions and/or from multiple batch
workloads. In such cases, merging the independent loads from three
drives to one without adequate PAV addresses could easily introduce
significant to severe device busy usage and IOSQ delay times. Without
knowing something about the concurrent 3390-3 volume usage patterns,
response time on 3390-9 without PAVs is a crapshoot even with only a
single large VSAM dataset.
--
Joel C. Ewing, Bentonville, AR [email protected]
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