hard drive benchmark question...

[Humate]

I have 12*500GB 7200.10 drives in raid6. I am using windows xp which only handles 2TB partitions. So, i have autocarving turned on in my raid contoller settings. Each carve is 2TB. When i run HDtune i get the following results:

HD Tune: AMCC 9650SE D0rv00a Benchmark

Transfer Rate Minimum : 14.3 MB/sec
Transfer Rate Maximum : 125.7 MB/sec
Transfer Rate Average : 91.4 MB/sec
Access Time : 10.0 ms
Burst Rate : 112.8 MB/sec
CPU Usage : 10.0%


This seems low to me. Is it because the hdtune benches essentially only 2TB, ie 4 drives worth of the array instead of all 12 ? Or is this result what would be expected ? I know raid6 isnt designed for performance, but i was expecting better. I use an amcc 3ware 9650se12ml raid controller which on their webpage states can do 800MB/s RAID 6 reads and 600MB/s RAID 6 writes. However, it doesnt state which model can achieve these read/write speeds, presumably it is the 24 port version, whereas i have the 12port model.

 

[rpstewart]

That is a bit low, I get over 200MB/s average from an 8 disk RAID5 array and that's 250Mb Hitachi T7K250s on a RocketRaid 2320 so hardly a high performance setup.

When it comes to reads RAID6 (and 5) is just a RAID0 array with a couple of unused stripes per block, there's no processing needed really to stick it together so reads should be pretty rapid. With 12 7200.10s it should be flying.

There are a few things to look at:

Have you tried HDTach? Sometimes it can give different results.

Do the drives have NCQ enabled? Turning it off for all the drives in my array improved the benchmark speeds by 25-30%.

Can you stick a screenshot of either HDTune or HDTach up so that I can have a look at the shape of the trace.

 

[Humate]

HDtune NCQ enabled



HDtach (quick bench (8mb zones)) NCQ enabled



HDtune NCQ disabled



HDtach (quick bench (8mb zones)) NCQ disabled



disabling whatever the hell NCQ is has increased performance a little. it still seems low to me.

 

[rpstewart]

disabling whatever the hell NCQ is has increased performance a little. it still seems low to me.

NCQ is Native Command Queing - a SATA function which allows the drive to re-order I/O requests to produce an optimised I/O queue which reduces the amount of head movement in an effort to improve performance. Unfortunately the RAID controller is asking for data in a specific order and NCQ can interrupt things by re-ordering requests forcing the controller to wait for the blocks it needs.

Still not sure why the transfer rates are low though. There isn't a huge amount of help on Google....

 

[Humate]

im not sure either. i might contact amcc tommorow and see what they have to say.

thanks for the NCQ tip... NCQ is off and staying off