We just purchased a new 24 drive RAID array and an
LSI 9285-8e RAID controller.
We are seeing 2 things which seem strange to us.
Write speeds are faster than read speeds (with either
There is a knee in the read speed such that when then read size (with
dd) is greater than 128Kbytes, performance drops by about 30%.
Here are the latest test results with
512k byte RAID stripe size, and
dd bs=1024k if=junk of=/dev/null => 9.11s = 1.4 GB/s dd bs=512k if=junk of=/dev/null => 9.38s = 1.3 GB/s dd bs=256k if=junk of=/dev/null => 9.78s = 1.3 GB/s dd bs=128k if=junk of=/dev/null => 7.03s = 1.8 GB/s dd bs=64k if=junk of=/dev/null => 6.77s = 1.9 GB/s dd bs=32k if=junk of=/dev/null => 6.79s = 1.9 GB/s dd bs=16k if=junk of=/dev/null => 6.49s = 1.9 GB/s dd bs=8k if=junk of=/dev/null => 6.91s = 1.8 GB/s dd bs=4k if=junk of=/dev/null => 6.46s = 1.9 GB/s
(FYI, for all sizes shown above, write speed is 2.2 GB/s)
I'm currently using RAID0, but I had almost identical results with RAID6.
It's just the new server being installed. No other apps running and no network connection causing any interrupts. This install is on OpenSuSE 11.4. We could do random read tests, but since our intent is to stream video (eg, 4K 3D, or 8K), we are really only worried about sequential reads.
Any ideas how to speed up the read speed?