Re: [Moosefs-users] SSDs

[Chris P. <ch...@ec...>]

On 2012/03/30 7:41 PM, Steve Thompson wrote:
> 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.

Hi Steve

Do those servers have bettery backed cache on the raid?  If so, are they 
set to write-back or write-through?

I have found that when running on standard SATA disks, the constant 
fsync is what slows things down tremendously.  A battery backed 
write-back cache on the raid card would help a lot there.

Chris