[Lustre-discuss] parity raid on MDTs

[John White]

Hey Folks,
	So we've got an interesting question.  We're looking at various MDT  
solutions for a small (120TB) filesystem.  We recently have been  
testing out some Intel X25-Es and are getting mind-blowing performance  
out of them and think they'd be perfectly positioned for an MDT.  We  
have some options here to consider and wonder if anyone has any insight.

We have some dell 2950's on site (6 bay).  One thought it fully  
populating a 2950 and using raid5/6.  Now, I know many of you are  
gasping right now, but I wonder if anyone has done the testing already  
for something like this.  Does the drastic cut in latency to the disk  
negate the XOR latency inherent in parity RAID?

Our other option is just getting an 8 bay 2970 and doing RAID10,  
something we don't have so much hesitation with but would require the  
purchase of extra hardware.

Thoughts?
----------------
John White
HPC Systems Engineer
(510) 486-7307
One Cyclotron Rd, MS: 50B-3209C
Lawrence Berkeley National Lab
Berkeley, CA 94720