7.1-PRERELEASE: arcmsr write performance problem

[Jan Mikkelsen]

David Kelly wrote:
> 
> On Dec 1, 2008, at 11:45 PM, Jan Mikkelsen wrote:
> 
>> Replying to my own post ...
>>
>> I have done a test on the same machine comparing 6.3-p1 to 7.1-PRE.  
>> The performance is the expected ~6MB/s (because of the lack of cache) 
>> on 6.3-p1, so the BIOS change doesn't seem to be at fault.
>>
>> This seems to be a regression somewhere between 6.3 to 7.1.  The Areca 
>> driver is the same in 6.3 and 7.1, so the problem seems to be elsewhere.
>>
>> I think this is more than just a "performance" problem.  The 
>> observations with gstat showing extremely high ms/w values (I have 
>> seen them as high as 22000) makes it look like IO completion 
>> interrupts are being lost.
>>
>> Any suggestions on where to look next?  Are there obvious candidates?
> 
> 
> ATA maximum block transfer has dropped from 128k to 64k in 7.x. Am not 
> sure where the handle is to tweak it back up but has slowed peak thruput 
> on my Dell PE400SC. Can watch with "systat -v"

Interesting, thanks.

> Worse, I have a stripped array of 2 drives that won't transfer more than 
> 43k at a chunk because apparently the stripe metadata didn't align 
> nicely on 64k multiples.

I know the partitions start at 64kB multiples in my case.  I did, 
however, reduce the RAID-6 stripe size to 4kB (from 64kB) and that 
improved things slightly, but the throughput on 7.1 is still slower by 
about a factor of a about 6 (measured by untaring ~3GB across ~167k 
files into a fresh filesystem).  And on 7.1 the machine is unusable 
during much of the time.

> -- 
> David Kelly N4HHE, dkelly at HiWAAY.net
> ========================================================================
> Whom computers would destroy, they must first drive mad.