topic Re: EVAperf averaging in Disk Enclosures

EVAperf averaging

Jeremy C — Thu, 06 Aug 2009 13:41:40 GMT

The EVAperf documentation says that for EVA 4k/6k/8k, if you do continuous polling at every minute (for example) then the results are actually the average for that minute that had just passed.

If you run:
evaperf hps -cont 60 -dur 60

You will get two sets of results. The first set of results immediate. It then waits 60 seconds and outputs the 2nd set of results.

My question is regarding that first set of results that are output. Are they an average of the previous 60 seconds (before the command was executed) or an instantaneous reading? If it's an average, that implies that a backlog of stats are stored somewhere constantly. What if I were to do an hourly reading? I doubt the averages of the past hour are being stored somewhere.

Re: EVAperf averaging

ks6542 — Thu, 06 Aug 2009 13:52:49 GMT

It dosent shows average of previous 60 second.

I.E

evaperf cs â cont 60 -dur 7200

It states multiple execution instances with 60-second sample intervals with two-hour duration.

Re: EVAperf averaging

Jeremy C — Thu, 06 Aug 2009 13:55:46 GMT

But every sample after the first is an average of the last N seconds (60 in our examples), unless I'm misinterpreting the docs.

Re: EVAperf averaging

Jeremy C — Thu, 06 Aug 2009 14:00:22 GMT

Thought I'd quote my source:
http://h71028.www7.hp.com/ERC/downloads/5983-1674EN.pdf?jumpid=reg_R1002_USEN

Page 5:
"Long sample intervals on the HP StorageWorks Enterprise Virtual Array 4000 (EVA4000), HP StorageWorks Enterprise Virtual Array 6000 (EVA6000), and HP StorageWorks Enterprise Virtual Array 8000 (EVA8000) will show less variation because of averaging over the sample interval."

Re: EVAperf averaging

ks6542 — Thu, 06 Aug 2009 14:20:37 GMT

Well it also shows multiple execution of the instances.. depend on what interval you run..

Seems confusing to me how it gonna avg the data from sample interval .. :(

Re: EVAperf averaging

Jeremy C — Thu, 06 Aug 2009 15:11:02 GMT

I think this explains it better (from page 7 of same document):
"The counters are managed somewhat differently in HP StorageWorks Enterprise Virtual Array 3000 (EVA3000) and HP StorageWorks Enterprise Virtual Array 5000 (EVA5000) systems than in EVA4000, EVA6000, and EVA8000 systems. In EVA3000 and EVA5000 systems, most counters (Req/s, MB/s, and so on) are one-second averages per sample, regardless of the interval between samples. Therefore, each sample represents an instantaneous snapshot of the activity at that moment. In EVA4000, EVA6000, and EVA8000 systems, however, the counters are true averages over the sample interval, so highly variable data will have different characteristics for longer samples than for shorter."