Disk read performance problem with PE2650 and Redhat AdvancedServer products.....

Gary Mansell Gary.Mansell at ricardo.com
Fri Oct 10 10:32:12 CDT 2003


My PE2650 comes with an Adaptec SCSI controller for the system disk RAID
so I presume that it needs to use the aacraid module?

On Fri, 2003-10-10 at 16:25, Diego_Leccardi at Dell.com wrote:

> Hi Gary,
> Try to use the megaraid_2002 driver instead of the megaraid one; this driver
> is only available on RH AS.
> 
> 	Diego
> 
> -----Original Message-----
> From: Gary Mansell [mailto:Gary.Mansell at ricardo.com]
> Sent: 10 October 2003 14:39
> To: linux-poweredge at dell.com
> Subject: Disk read performance problem with PE2650 and Redhat
> AdvancedServer products.....
> 
> 
> Dear all,
> 
> 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
> PERC 3Di, The external RAID unit is an EMC FC4500 with 9x73GB disks in a
> RAID 5 configuration. The RAID unit is connected using a QLogic QLA2310
> FCAL card.
> 
> When I originally bought the machine I found a read performance problem
> with RH AS 2.1 (fully up2dated) and had to install RH Linux 7.3 which
> did not seem to have the same problem. I found that reads from both my
> external RAID unit and the internal PERC mirrored system disks were
> awfully slow - about three times slower than with Redhat Linux. There
> was definitely something wrong somewhere as reads were slower than
> writes to the same device!
> 
> The time has now come to add another 1TB of disk to the array and at the
> same time I would like to upgrade the system to RH AS 3.0. I have built
> a spare PE2650 with RH AS 3.0b2 and have found that the disk read
> performance is still a problem with the internal PERC mirrored system
> disk. I have not been able to test it against the external FC4500 as it
> is used continually on the production system.
> 
> I have tried further tests in an effort to isolate the cause:
> 
> 1) I have installed RH 9.0 on the spare PE 2650 described above and this
> does not exhibit the read performance problem.
> 2) I have built a desktop Viglen PC with RH AS 3.0b2 and this does not
> exhibit the read performance problem with either it's IDE system disk or
> an externally attached SCSI disk or an externally attached Software RAID
> 0 set.
> 3) I have built the PE 2650 with RH AS 2.1 and see the read performance
> problem with the internal PERC mirror but not with an external single
> SCSI disk or an external Software RAID 0 set.
> 
> On the surface, it would appear that RH AS products have trouble reading
> from HW RAID devices whereas the community versions of RH Linux do not.
> This makes no sense to me though as the PERC system mirror is just
> presented as a SCSI disk to the O/S via the aacraid module and the
> external HW RAID 5 device is presented as a SCSI disk to the O/S via the
> qla2300 module.
> 
> Any suggestions as to what the problem could be would be gladly
> appreciated as I am starting to pull my hair out here now.

-- 

Gary Mansell
Technical Computing Team Leader
IT Department
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