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SubjectRe: Where is the performance bottleneck?
On Mon, 29 Aug 2005, Mark Hahn wrote:

>> The U320 SCSI controller has a 64 bit PCI-X bus for itself, there is no other
>> device on that bus. Unfortunatly I was unable to determine at what speed
>> it is running, here the output from lspci -vv:
> ...
>> Status: Bus=2 Dev=4 Func=0 64bit+ 133MHz+ SCD- USC-, DC=simple,
>
> the "133MHz+" is a good sign. OTOH the latency (72) seems rather low - my
> understanding is that that would noticably limit the size of burst transfers.
>
I have tried with 128 and 144, but the transfer rate is only a little
bit higher barely measurable. Or what values should I try?

>
>> Version 1.03 ------Sequential Output------ --Sequential Input- --Random-
>> -Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
>> Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
>> Raid0 (8 disk)15744M 54406 96 247419 90 100752 25 60266 98 226651 29 830.2 1
>> Raid0s(4 disk)15744M 54915 97 253642 89 73976 18 59445 97 198372 24 659.8 1
>> Raid0s(4 disk)15744M 54866 97 268361 95 72852 17 59165 97 187183 22 666.3 1
>
> you're obviously saturating something already with 2 disks. did you play
> with "blockdev --setra" setings?
>
Yes, I did play a little bit with it but this only changed read performance,
it made no measurable difference when writting.

Thanks,
Holger

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