Operating System - Tru64 Unix
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Re: Collect I/O stats report

 
Rob Urban
Advisor

Re: Collect I/O stats report

I am the original author of collect. I haven't maintained it for years, but I still know something about the data-collection landscape at digi.., uh, compa, uh, HP. Collect isn't always correct, because it's situated directly on top of kernel data-structures, and they have a nasty habit of changing from release to release. However, mostly, collect is correct, and if collect can't give you the info, it's very unlikely that anything else can, with the exception of some subsystems that have data-extraction tools build by the same groups that develope the kernel subsystems, for example lsm and advfs. iostat was never very useful, because nobody loved it, and sar, sigh, was a miscarriage. When I left Digital ('99) monitor was already
falling behind with respect to Tru64.

Part of the problem with collecting I/O data is that it may not be properly maintained in the kernel, which means you're SOL not matter what tool you use.

Collect is the best tool for disk I/O.

cheers,

Rob Urban
Johnny Vergeer
Occasional Advisor

Re: Collect I/O stats report

After a hardware & firmware upgrade and PK5 install on the system, we had some spare time in the maintenance slot.

We ran the "I/O test" described above, and with the system totally idle, we recorded a worst case of 0.55 seconds during a 45 minute test period.

I would think that this is quite high for a system without any load?
Han Pilmeyer
Esteemed Contributor

Re: Collect I/O stats report

That's quite a better number than what you described before (between 8 and 20 seconds). I will agree with you that this is still not a number that we would like to see.

Could you give more details about the results of the test:
- You say that this is using the same test. Is this reproducable?
- Is it always on the same disk?
- Is the EMC also idle (during the maintenance window) or are other systems using it?
- Are the disks behind the LUN dedicated to the test?
- What did the EMC performance investigation reveal?
- etc.
Christof Schoeman
Frequent Advisor

Re: Collect I/O stats report

Hi

To answer some of your questions:
- Reproducable? Kind of. Under load, we see the 8 to 20 delays, every time. Without load, we don't see these delays.
- We see this on all the disks, at different times.
- No, the EMC is busy serving other systems all the time.
- No, the disks (spindles) serve other hosts as well.
- While our test reported an I/O that took about 10 seconds to complete, the EMC test didn't show any I/O that took more than a second to be served.

This issue has been escalated within HP. We are expecting some assistance with our investigation.

I'll be sure to post our findings.