Hi there,
I have a very serious issue with an MD3800i (dual controllers) that I have just purchased. I have an MD1200 expansion array attached. I am getting expected write performance (800mb/sec+) however I'm getting around 2mb/sec reads.
I have tried changing cache settings, creating smaller LUNs, multiple host OS's (xen/vmware/hyper-v), I've tried MPIO and fixed/single target and nothing makes a difference. I have dual controllers and I have tried fixing to each controller individually and still no change (so isn't a controller at fault). I have changed the block size, I have taken the switch out of it and connected directly to the SAN, I have tried disabling prefetch, everything I can think of. This is stopping me from configuring my new environment and is making my investment seem like a bad choice.
I have noticed that when I read a file from the SAN, the disk latency flies up to around 30ms. I have also noticed that for around 1s at the very start, the read speed is very quick and then drops down to the awful performance.
I have tried to do some fixes I found on the internet regarding setting the cacheFlushStart and cacheFlushStop however the cacheFlushStop command has been deprecated in a later version of the firmware so I cannot try this fix. The fix by wallewek sounded promising until the firmware wouldn't let me do it!
I cannot believe that this SAN can only read at 2mb/sec (sometimes I can get as high as 20-30mb/sec with MPIO, but this is still not acceptable!). I have a very old iSCSI SAN with gigabit links that max out at 100mb/sec+ so something is wrong here.
Any help would be appreciated - I'm lost as to what to do now next now as I feel like I've tried everything possible. I have spent over a week trying everything I can see and think of and I'm getting nowhere.
Thanks