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E200i RAID Controller Performance

 
Dave Huttner_1
Occasional Contributor

E200i RAID Controller Performance

Hello,

I am doing some performance monitoring to try to see if there is a performance bottleneck in our RAID/Disk setup on our SQL 2005 Server. Our web based app is running slow. We are using a E200i RAID controller with the 128 MB BBUC option. We have the controller set with a 50/50 read/write cache ratio and the hard drive's cache is enabled on all drives.

We have two RAID sets. The first is a RAID 1 set with two, 15K rpm SAS hard disks where the OS and SQL log files are stored. The second ia a RAID 5 set with four, 15K rpm SAS hard disk where the SQL data files are stored.

Our Disk Transfers/sec are averaging 135 with a max of 2053. Our Avg. Disk Queue Length is averaging .606 with a max of 32.75. Memory, paging and CPU utilization are low.

I know that the E200i is on the low end of the totem pole for RAID controllers. I am wondering if I'm asking too much of it and need a higher end controller. My reading seems to say that a our .606 Avg. Disk Queue Length is good as long as it is under 2. My reading also says that we should be averaging below 25 Disk Transfers/sec and we are at 135. This is the only number that concerns me. In my thinking though, since my Avg. Disk Queue length is low, isn't the RAID/hard drives working fast enough? If you have data to write to disk, it has to be written, no matter how much you have. Since we have a high Disk Transfers/sec but a low Disk Queue length, isn't this good and the RAID/Disk setup is working well?

Any E200i or disk/RAID performance advice/experience would be greatly appreciated.

Thank you in advance...
Dave
1 REPLY
u84823
Regular Advisor

Re: E200i RAID Controller Performance

Check your controller cache is in write-back mode. Ensure disk level caching is read-only, write caching at the physical drive level is dangerous.

135 IOPs is pretty low for a 4-drive 15k SAS raid-5 array, which should do about 500 IOPs. However it might be indicative of some bad SQL in your app - I would review execution plans to check to FTS or double passes (i.e. select * from..., count *...).

If however you do need more disk throughput, your options are to expand the array onto additional disks (if you have space for them), upgrade to 512MB BBWC, and finally replace the controller with something better. The raid-5 write performance of the E200 is pretty bad, about 30MB/s IIRC.

HTH