Feedback solicited - read performance is awful with PE2650 runningRH AS

Wayde Nie niew at
Tue Oct 21 16:08:00 CDT 2003


I've got a PE2650 running RHAS3b2. It has 4-36Gb disks in 2 HW mirror
sets (presented as sda and sdb) on a PERC3Di (Adaptec aacraid driver).
The box has 2x 2.4GHz Xeon's with HT enabled and 2Gb RAM.

The dd test results as follows:

[root at feweb tmp]# /usr/bin/time dd if=/dev/zero of=./testfile bs=16384
250000+0 records in
250000+0 records out
0.29user 47.06system 6:35.95elapsed 11%CPU (0avgtext+0avgdata
0inputs+0outputs (138major+15minor)pagefaults 0swaps
~10.34 Mb/s Write rate.

[root at feweb tmp]# /usr/bin/time dd if=./testfile of=/dev/null bs=16384
250000+0 records in
250000+0 records out
0.21user 17.91system 3:03.71elapsed 9%CPU (0avgtext+0avgdata
0inputs+0outputs (137major+18minor)pagefaults 0swaps
[root at feweb tmp]#
~22.26 Mb/s Read rate.

> ----------------------------------------------------------------- <
> Wayde Nie                                                         <
> Software Analyst               Computing and Information Services <
> phone: (905)525-9140 ext 23856 McMaster University, CANADA        <
> fax:   (905)524-5288           niew at                   <
> ----------------------[\]--->=\o.:---[\]------------------------- <

On Tue, 2003-10-21 at 07:17, Gary Mansell wrote:
> I would really appreciate some help from the list here to see if anyone
> else is suffering from the same problem that I am. I appear to have
> fallen foul of a problem with RH AS products running on Dell PE2650's.
> I have raised bug number #106771 at and I
> have tried to raise the issue with Dell but I am not getting very far -
> both parties blame the other and I am stuck in the middle getting
> nowhere.
> I have installed RH AS 2.1 and RH AS 3.0b2 and have found that the read
> performance from the system mirror is awful - it is less than the write
> speed!! If I install RH 9.0 or RH 7.3 the read performance to this same
> device is fine.
> Please could anyone who has a Dell PE2650 with a version of RH AS
> installed run the following quick and dirty (but representative) disk
> performance tests and let me know if they find the same.
> Write Performance:
> /usr/bin/time dd if=/dev/zero of=/testfile bs=16384 count=250000
> Read Performance:
> /usr/bin/time dd if=/testfile of=/dev/null bs=16384
> FYI, I have a Dell PE2650 with 2x 2.4GHz Zeons (Hyperthreading enabled),
> 2GB RAM, 2x18GB internal system disks in a HW mirror configuration using
> the Adaptec PERC 3Di.

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