Read Performance problem with Advanced Server 2.1 and PE2650

Gary Mansell GRMansell at ricardo.com
Thu Dec 12 06:25:00 CST 2002


Dear all,

I have just taken delivery of a Dell PE2650 which I am using as an NFS/SMB fileserver for a mixture of about 100 UNIX and NT client workstations. The machine has 2x2.4Ghz processors, 2Gb RAM, 2x18Gb system disks in a hardware mirror configuration, A 500Gb EMC FC4500 storage array configured for RAID 5 attached via two Qlogic QLA2310F HBA's (note: it is not possible to use both cards in a load balanced/failover configuration until Dell release Powerpath for Linux). It also has a Ultrium Autoloader device connected via an Adaptec SCSI card.

It was originally intended that I run the machine using the Redhat Advanced Server 2.1 Operating System up2dated to the latest software revisions. Before going live, I performed some simple 'dd' IO tests and some more complex IOzone benchmarks and found a glaring problem with IO performance of this configuration - the read performance from the FC4500 was surprisingly low. It was even found to be lower lower than the write performance, which for a RAID 5 device is obviously wrong! I checked this with the read and write performance to the internal SCSI disks in a hardware mirror configuration and found the results to be the same.

I then tested the machine using Redhat 7.3 up2dated with the latest software revisions and found performance to be more like what I expected. ie the read performance was better than the write performance and the figures where higher.

Hence, I have now gone 'live' with a Redhat 7.3 server instead of the Advanced Server 2.1 that I purchased from Redhat for £1500. Please can someone explain to me what is going on here. I understand from colleagues that they have found this to also happen on HP/Compaq hardware. I would also like to know if there is expected to be a fixed version of Redhat Advanced server anytime soon?

Disk Performance results summary:

						RH AS		RH 7.3
RAID 5 FC4500		Write		50MB/s		53MB/s
				Read		28MB/s		74MB/s

RAID 0 FC4500		Write		Not tested		70MB/s
				Read		Not tested		84MB/s

HW RAID 1 Int SCSI	Write		28MB/s		32MB/s
				Read		25MB/s		63MB/s





Gary Mansell
Senior Technical Analyst
IT Department
Ricardo Consulting Engineers




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