We have recently moved our database to a SAN and I am trying to monitor performance. Does anyone know of a good way to monitor performance going to the SAN? I have been watching things like %Disk time and Avg Disk Queue Length, but does anyone know if these are acurrate when referring to a SAN? My %Disk Time is going up to numbers as high as 1200. The Disk queue length seems kind of low for seeing that high disk time as well.
I a junior DBA here and the senior dba in charge of our sql cluster monitors disk write bytes/sec, disk read bytes/sec, and average disk queue length among others things and I'm pretty sure our stuff's on a SAN. He says anything approaching 1 or above for queue length is cause for alarm. I think read & write throughput are specific to the hardware.
So what the performance monitor is telling you is that your disk is writing twelve times as fast as it can (not real likely using conventional hardware, but it happens frequently using a SAN). That would tend to lead to really short disk queue lengths.
I'd suggest that you talk to your SAN vendor. They should be able to give you some really good ideas on what you can monitor, especially within the SAN drivers themselves (if you are using SAN specific drivers).
You obviously have to adjust any counters delivered with the OS, since they are tuned for a very different world than a SAN. A good first guess is to scale the stock values by about a factor of 20, but you'll probably have to adjust that once you get a better feel for how your particular configuration performs.
We already did ask the SAN vender and they told us to purchase this software package they created to monitor performance. Personally I don't think that is necessary, so I was hoping I could monitor performance through these counters. I just don't know how they should be adjusted for the SAN.