Re: below 10MB/s write on raid5

[Justin Piszcz <jpiszcz@lucidpixels.com>]

On Tue, 12 Jun 2007, Bill Davidsen wrote:

> 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
>
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I was the one who tried > 32768 it crashed the machine (on an older box).

Justin.