[Lustre-discuss] RAID Stripe alignment

Kaizaad Bilimorya kaizaad at sharcnet.ca
Mon Dec 6 08:44:02 PST 2010


Hello,

I read this thread
http://www.mail-archive.com/lustre-discuss@lists.lustre.org/msg07791.html

and the Lustre Operations manual "10.1 Considerations for Backend Storage"

in order to determine the best performing setup for our OSS hardware.

HP DL180 G6
- CentOS 5.5 and Lustre 1.8.4
- HP Smart Array P410 controller (512 MB cache, 25% Read / 75% Write)
- 600 GB SAS drives

The stripesizes (in HP P410 terminology is the amount of data read/written 
to each disk) available on the P410 array controllers are 8,16,32,64,128,256

Two of the scenarios that we tested are:

1) 1 x 12 disk RAID6 lun
chunksize = 1024 / 10 disks = 102.4 => use stripesize=64
- not optimally aligned but maximum space usage
- setup on oss[2-4]
- sgpdd_survey results:
   http://www.sharcnet.ca/~kaizaad/orcafs/unaligned.html

2) 1 x 10 disk RAID6 lun
chunksize = 1024 / 8 = 128 => use stripesize=128
- optimally aligned but at the sacrifice of 2 disks of space
- setup on oss[8-10]
- sgpdd_survey results:
   http://www.sharcnet.ca/~kaizaad/orcafs/aligned.html


In our cases, the graphs seem to indicate that the the underlying RAID 
alignment setup doesn't matter much, which is totally counter intuitive to 
the recommendations by the Lustre list and manual.

Is there something we are missing here? Maybe I misunderstood the 
recommendations? Or are we just bottlenecking on a component in the setup 
so a proper RAID alignment doesn't show as being beneficial? Any insight 
is appreciated.

thanks
-k



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