Yes, you are right.
However I observed benefits on DASD array connected using 8 channels
FICON Express16S+ with utilization below 10%.
BTW: it was all flash array with big cache.
However you mentioned important thing, which I didn't mention - whole
process "from memory to disk". I mean MVS, IOS logic, channel programs,
etc. One of reliefs done in the past are 3390B - alias devices, then
HyperPAV, MIDAW, zHPF.
--
Radoslaw Skorupka
(looking for new job)
Lodz, Poland
W dniu 10.03.2021 o 09:31, Colin Paice pisze:
One of the benefits of striping is that you can do I/O in parallel, for
example have 4 concurrent I/Os, so you reduce the "connect time" for
transmission of data.
Once the data gets to the end of the cable into the Storage Controller, it
tends to be caught in cache, and should not matter what happens in the
storage controller and onto the disk.
On Tue, 9 Mar 2021 at 21:45, Radoslaw Skorupka <[email protected]>
wrote:
W dniu 09.03.2021 o 18:21, Paul Gilmartin pisze:
On Tue, 9 Mar 2021 12:42:34 +0100, Radoslaw Skorupka wrote:
Striped PS datasets (extended format PS) are managed by IEBGENER,
ICEGENER or IDCAMS as regular (non-striped) datasets. I mean user
perspective.
In other words, transparent to the utility or user program, with at
most changes to SMS profile?
Yes, you have to define it in SC. And use extended format.
What's the maximum performance boost? "Linear" can't mean
"infinite". Limited by channel, main storage, controller cache ...
bandwidth. (Model-dependent, of course.)
It depends. I remember loooooong discussion (read: quarrel) with my
co-worker. It was 20+ years ago and it was about sense of striping on
RAMAC RVA. He was right. ;-) Striping gave some performance gain. I
can't remember exact values, but adding further stripes didn't help.
One may say for real (old gone) 3390 volumes the performance gain was
rather obvious, but bunch of volumes emulated on same hardware -
controller, disk RAID group - it should be no difference whether you use
one or several emulated volumes. However it is UNTRUE. Tested many times
on various disk system models. And sometime you can deep dive in disk
system details and create storage group consisting of volumes from
different RAID groups, possibly server by different controllers
(electronics). Modern arrays have quite reasonable features to support it.
And2: even volumes defined on exactly same physical resources perform
better when striping is in effect.
This would appear to be a solution for the OP. Of course, unless
he's already experiencing it, perhaps unbeknownst.
Good to consider. However striping is the best for (long) sequential
read or write operations.
Last, but not least: it is easy to test.
BTW: Striping and multi-volume and extents is quite interesting issue
for quiz. ;-)
Things changed with the z/OS releases and the rules are different for
ef-PS and VSAM.
When I teach it on VSAM course, people usually forget about VSAM and
discuss about PS.
--
Radoslaw Skorupka
(looking for new job)
Lodz, Poland
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