Re: Poor read performance on high-end server

[Jens Axboe <axboe@kernel.dk>]

On 2010-08-05 16:51, Chris Mason wrote:
> And then we need to setup a fio job file that hammers on all the ssds at
> once.  I'd have it use adio/dio and talk directly to the drives.  I'd do
> something like this for the fio job file, but Jens Axboe is cc'd and he
> might make another suggestion on the job file.  I'd do something like
> this in a file named ssd.fio
> 
> [global]
> size=32g
> direct=1
> iodepth=8

iodepth=8 will have no effect if you don't also set a different IO
engine, otherwise you would be using read(2) to fetch the data. So add
ioengine=libaio to take advantage of a higher queue depth as well.

Also, I didn't see Chris mention this, but if you have a newer intel box
you can use hw accellerated crc32c instead. For some reason my test box
always loads crc32c and not crc32c-intel, so I need to do that manually.
That helps a lot with higher transfer rates. You can check support for
hw crc32c by checking for the 'sse4_2' flag in /proc/cpuinfo.

-- 
Jens Axboe