Description of problem: Comparing the Fibre Channel read/write performance to a direct attached JBOD disk, seeing decreased read performance on EL3.0 as compared to AS2.1. Seeing the same results if using a QLogic or Emulex HBA. So I can only assume that this is a Red Hat issue. My Results: AS 2.1 Read dd if=/FCdisk1/data of=/dev/null bs=100k 40-41MB Write dd if=/data of=/FCdisk1/data1 bs=100k 0-15MB AS 3.0 Read dd if=/FCdisk1/data of=/dev/null bs=100k 19-20MB Write dd if=/data of=/FCdisk1/data1 bs=100k 34-35MB Notice that the read performance on AS3.0 is about half the write performace. I get similar performance results if using Bonnie. I only mention that because with the dd command, it only allows or does one outstanding request at a time. Several of our customers have also seen this problem and we direct them to Red Hat. Can anyone explain why this is occurring and if there are some configuration settings, or patch to increase or make the performance number more consistent? Thanks, Randy Version-Release number of selected component (if applicable): How reproducible: Steps to Reproduce: 1. 2. 3. Actual results: Expected results: Additional info:
Which RHEL 3 kernel version are you using? There are some performance improvements in Update 4. U4 is in beta now, and is due out in December. Please re-test with U4.
I'll add Update 4 and retest. I've never done an update before, where do I find it since U4 is still in beta?
Instructions sent by email.
Randy reports that he can not reproduce this problem on U3: "I re-installed AS 3.0 on the same system and still not seeing the read performance issues and I had previously. Getting about the same read (50MB/sec) and write (54MB/sec) performance." He has not tried U4. Closing this BZ. Reopen if the problem reoccurs.