Re: [Moosefs-users] SSDs (was: fox and bird)

[Steve T. <sm...@cb...>]

On Fri, 30 Mar 2012, Ricardo J. Barberis wrote:

> Do those drives happen to have 4 KB physical block size?
> That combined with unaligned partitions could explain such bad performance.

I always use whole disks combined into RAID sets via hardware raid, so 
partition alignment is not an issue, and then use ext4 file systems as 
chunk volumes. Raw I/O performance of the volumes are excellent, and 
indeed the I/O performance numbers shown by the MFS cgi script are also 
excellent (both read and write are greater than gigabit bandwidth). I use 
high-end Dell servers with 3+ GHz processors and dual bonded gigabit links 
for I/O, but nevertheless the resulting MFS I/O performance, which was 
good initially when I built a testing setup, has just plummeted with a 
real-world I/O load on it, to the point where I am getting a lot of 
complaints. This looks like a show stopper to me, which is somewhat 
upsetting. I'm not sure what I can do at this point to tune it further.

Steve
-- 
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Steve Thompson, Cornell School of Chemical and Biomolecular Engineering
smt AT cbe DOT cornell DOT edu
   "186,282 miles per second: it's not just a good idea, it's the law"
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