evaperf question

[Tim Chilton]

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?

[Víctor Cespón · Accepted solution]

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]

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]

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]

That's exactly the information I was seeking! Thanks!

[Tim Chilton]

Assigning points and closing thread.