evaperf question

 
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Tim Chilton
Frequent Advisor

evaperf question

I understand how to pull data with evaperf, but is there a document out there that describes what values are acceptable and what indicate an issue for an EVA8100?
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Víctor Cespón
Honored Contributor
Solution

Re: evaperf question

http://h71028.www7.hp.com/ERC/downloads/5983-1674EN.pdf

In a disk group:
Write latency < 5 ms
Read latency < 15 ms

Mirror por traffic < 100 MB/s

If those values are exceeded, then you need to investigate each vdisk and port to see where the traffic comes from and where it goes.

Tim Chilton
Frequent Advisor

Re: evaperf question

Thanks! I do have one further question and the PDF you linked me to wasn't clear. You indicated that write latency in a disk group should be <5ms and read latency should be <15ms. Is that for the physical disk group (pdg) object or the virtual disk group object (vdg)? The reason that I ask is that the virtual disk group is showing avg read miss latency of 6.6 or less and average read hit latency of 1 or less. The physical disk group object is showing an average write latency for one controller of 10.4ms and on the other controller 0ms with read latency of <1 across the board. So if the values you quoted are for the VDG object, I'm fine. If they are for the PDG object, I have a problem. I ahve attached the output of an evaperf all if you're interested.
Víctor Cespón
Honored Contributor

Re: evaperf question

Those values were for the virtual disk group, since they are what it's seen from the outside. The EVA has a cache, and this reduces the time it takes to perform a read or write.

The physical disk group values are the times it takes to really read or write to the disks, and they are always bigger. But the number of I/Os that reach the disks is a lot lower than the ones reaching the disk group (this is known as front-end and back-end transfers).

The writes are considered done once they reach the cache, so usually they take 1 ms or less. The read hits are sent from the cache, so they take very little time too. Only the read misses have to be fetch from the disks.
Tim Chilton
Frequent Advisor

Re: evaperf question

That's exactly the information I was seeking! Thanks!
Tim Chilton
Frequent Advisor

Re: evaperf question

Assigning points and closing thread.