Re: below 10MB/s write on raid5

[Bill Davidsen <davidsen@tmr.com>]

Dexter Filmore wrote:
> I recently upgraded my file server, yet I'm still unsatisfied with the write 
> speed.
> Machine now is a Athlon64 3400+ (Socket 754) equipped with 1GB of RAM.
> The four RAID disks are attached to the board's onbaord sATA controller 
> (Sil3114 attached via PCI)
> Kernel is 2.6.21.1, custom on Slackware 11.0.
> RAID is on four Samsung SpinPoint disks, has LVM, 3 volumes atop of each XFS.
>
> The machine does some other work, too, but still I would have suspected to get 
> into the 20-30MB/s area. Too much asked for?
>   

Increase your stripe cache size in /sys/block/mdX/md/stripe_cache_size. 
If you have a chunk size of 256, try setting the cache size to 8192 and 
see if your write performance ends up ~100MB/s or so.

   echo 8192 > /sys/block/mdX/md/stripe_cache_size

Where "X" is your array name, of course.

Note, larger values will help more, but it's definitely diminishing 
returns, so don't get carried away. There was a report of problems with 
size > 32768, I don't remember the details, so I would avoid that as well.

-- 
bill davidsen <davidsen@tmr.com>
  CTO TMR Associates, Inc
  Doing interesting things with small computers since 1979