Rob,
I have performance data from ESAMON; however, the format that it was
given to me I am unable to read (binary). Is there a way to read the
ESAMON data, collected on VM, on Linux x86? The only other data I have
is iostat -dkx which shows that there are some greater than expected
wait and service times for the DASD in question, by greater I mean 100s
and 1000s+.
Thanks!
Eric
Rob van der Heij wrote:
On 6/13/07, Eric and Barbara Sammons <[EMAIL PROTECTED]> wrote:
Looking into performance problems, in search of some ideas of what to
look for. I believe the issue may be related to the type of DASD
being used.
Fortunately there's instrumentation on the platform, and you need a
performance monitor to analyze your configuration and workload to
understand what is holding you back.
Scenario, dd command to generate a 1G file if=/dev/zero takes 15s on
x86_64 platform. The same command takes 15m on the s390x platform.
In my environment the command takes 16s. My environment leverages
MOD-3 DASD while the environment in question has MOD-9 and MOD-27
devices. I know historically the MOD-9 is typically a slower device
but I don't know much about the MOD-27.
The "slow" was for real 3390's. Modern DASD only emulates the number
of cylinders on the logical volumes, so a 3390-27 is not necessarily
slower than a 3390-3. However, since there is only one I/O active at
the same time to the logical volume, the subchannel might become a
bottleneck. Or phrased differently, when your workload is such that it
could run multiple I/O's in parallel, you might be able to take
advantage of providing the disk space in multiple logical volumes (and
thus multiple subchannels). Second best could be PAV in some
situations.
Your test is in general not enough to understand the capabilities.
After all, the mainframe was meant to run a lot in parallel and it
would be better to measure how many servers could be doing this test
at the same time without impacting each other heavily.
Is it truly possible that the performance of these devices is bad
enough to see such a difference between MOD-3 and x86_64 v. MOD-9 and
MOD-27? What else should / can I look at to determine the root cause
of the performance issues?
Your numbers look weird enough to be suspicious. Most likely your x86
platform has a huge amount of memory so it never even did a single I/O
to disk for your benchmark. If you were given a fairly small Linux
server on the mainframe, it suddenly had to do I/O and wait for that
to complete. Very different cases.
If you do 1 GB in 15 min, that's 1 MB/s. Still rather slow. First
you'd need to see whether this is ESCON or FICON. There may also be
other things holding back the virtual machine (like paging, CPU
contention, failure to drop from queue, etc).
Collect performance data and see what's going on.
Rob
--
Rob van der Heij
Velocity Software, Inc
http://velocitysoftware.com/
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