I have a meeting with DELL today to discuss some of our SAN setup and I want to be able to talk about what I am seeing. We have an average Latency of 20ms. I'm attaching a screenshot of what it is currently showing over an extended time range.
If there are any iSCSI SAN gurus out there, is what I'm looking at a problem? I think it is starting to show the signs of one. The Latency is across all the servers as well, and previously I thought it was just our main dataserver.
On a sidenote:
We have a PS5000 and PS6000 both set up as RAID 50. We are looking at recommendations for another container and it looks like it will be specifically for SQL so I'm thinking RAID 10. The only thing is that PS6000XV (which looks to be the best) will only give around 4.2 TB on RAID 10 at the most. I'm wondering if the RAID 10 will even give us the best performance as well.
Best Answer
Most of the major points are covered in the answers to the post gbjbaanb referenced in his comment but I would add some more to specifically address your questions.
Adding any PS series array to this will improve your performance - provided you let the EQL automatation to do its thing. A PS6000XV configured in RAID 10 will help most clearly but a 10K SAS PS6000X or even a 7.2k SATA II PS6000E will improve the overall IOPS available, add network paths and bandwidth. Any one of them will add at least 1000 IOPs to the overall capacity of your environment.
My opinion on Equallogic configurations is that you should avoid dedicating arrays to a single purpose - you will almost always find that overall performance is better if you allow the Equallogic Group to distribute volumes over as many arrays as it can, that way your systems can scale out a lot better. By dedicating arrays to a single volume or function you are limiting the total number of paths, bandwidth and amountof controller CPU available for those volumes.
The average IOPS (178) indicates to me that you're not really pushing the system's limits at all. Even with 7200rpm drives, only one controller (which I hope you don't have) a single array and RAID 5 you should not be stressing even a single PS array at that level, although I may be missing something here. You appear to have a 70:30 Read write ratio so RAID 50 is probably optimal for this use case.
I'm intrigued by the 20ms read latency number, your writes at 2ms seem to be OK but your reads are much higher than I'd expect. Are you sure there is nothing else going on? Disk failures\replication\huge numbers of snapshots?