7.1-PRERELEASE: arcmsr write performance problem

Richard Tector richardtector at thekeelecentre.com
Wed Dec 3 01:28:22 PST 2008

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"
> 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.

Would changes to ATA have affected arcmsr? As far as I know it is not 
linked to the ATA subsystem at all, though it would explain some odd 
instances of one of my machines becoming unresponsive a couple of times 
a day.

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