Bug 113171
Summary: | lousy read performance on megaraid with 2.4.21-4.0.2.EL | ||
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Product: | Red Hat Enterprise Linux 3 | Reporter: | Per Andreas Buer <perbu> |
Component: | kernel | Assignee: | Tom Coughlan <coughlan> |
Status: | CLOSED ERRATA | QA Contact: | Brian Brock <bbrock> |
Severity: | medium | Docs Contact: | |
Priority: | medium | ||
Version: | 3.0 | CC: | bb, dg, dledford, georgios, linux-sid, perbu, petrides, riel |
Target Milestone: | --- | ||
Target Release: | --- | ||
Hardware: | i686 | ||
OS: | Linux | ||
Whiteboard: | |||
Fixed In Version: | Doc Type: | Bug Fix | |
Doc Text: | Story Points: | --- | |
Clone Of: | Environment: | ||
Last Closed: | 2004-05-12 01:08:16 UTC | Type: | --- |
Regression: | --- | Mount Type: | --- |
Documentation: | --- | CRM: | |
Verified Versions: | Category: | --- | |
oVirt Team: | --- | RHEL 7.3 requirements from Atomic Host: | |
Cloudforms Team: | --- | Target Upstream Version: | |
Embargoed: |
Description
Per Andreas Buer
2004-01-09 09:09:07 UTC
doing /dev/sda IO is nor a realistic testcase since it avoids all filesystem optimisations that increase performance (eg no or little readahead etc etc etc) Going through the filesystem yields 20MB/s which still is way below expected results. A mediocre IDE-drive yields approx. 45MB/s. Linux 2.6 outperforms 2.4.21-4.0.2.EL grossly. It should not do so. I have also experienced the problem on a Dell 2650 with PERC 4 DC on a Power Vault. See http://marc.theaimsgroup.com/?l=linux-scsi&m=107408386620006&w=2 for some numbers georgios.no I also am having the same problem on a customers box, IBM Server Raid 6m + raid 1 and raid 1e running as a database server, only getting about 10-15 MB/sec, will redhat fix this problem or will i just have to use the stock 2.6 kernel ???? I tried the new kernel from RHEL ES 3 OU1 (2.4.21-9.EL). Still same read performance with megaraid2 driver (~10MB/s). Results consistent for both bonnie++ and dd tests. plain-vanilla 2.4.24 kernel does not show this performance problem. Penguin Computing 225 Dual P/III-1266 4GB RAM MegaRAID Express 500 (RAID1: 2x Hitachi DK32DJ-18MC, RAID5: 4xSeagate ST336607LC) MegaRAID 320-2 in Dell PV220S (RAID5+1: 6x Maxtor Atlas10k4_73SCA) system up2date as of today. Is there a RH recommended work-around for this issue? As Arjan said above, doing I/O to the device special file is not generally representative of real workloads. Consider these results, done on a Dell 1650 with a PERC3 and megaraid(1): # time dd if=/dev/sdc of=/dev/null bs=8k count=25600 25600+0 records in 25600+0 records out real 0m21.497s user 0m0.010s sys 0m2.120s => 9.5 MB/s - this reproduces your awful results, as above. Now assign the same device to raw1, and run the test again. # time dd if=/dev/raw/raw1 of=/dev/null bs=8k count=25600 25600+0 records in 25600+0 records out real 0m10.826s user 0m0.010s sys 0m0.290s => 18.8 MB/s - raw is twice as good, but still not great. Try it with larger I/Os: # time dd if=/dev/raw/raw1 of=/dev/null bs=64k count=3200 3200+0 records in 3200+0 records out real 0m4.544s user 0m0.000s sys 0m0.090s = > 44.4 MB/sec - not bad - larger I/O to the raw device produces reasonable results. Increase I/O size again: # time dd if=/dev/raw/raw1 of=/dev/null bs=256k count=800 800+0 records in 800+0 records out real 0m2.450s user 0m0.000s sys 0m0.120s => 82 MB/sec. The reason RHEL 3 is different from the stock 2.4 and 2.6 kernels is because of a performance tuning change that was done in RHEL 3. This change defers the combining of small I/Os into larger I/Os until later, when it can be done most efficiently (for some workloads). A disadvantage of this approach is that in some situations single-stream sequential I/O may not be combined at all. We are continuing to review the impact of this patch on real workloads. We will look at your iozone and bonnie++ results in more detail. If you have additional results for your actual workload we would be interested in reviewing them. Doug, this may be considered a duplicate of bug 104633. If you agree, you may want to mark it as such. Tom, you are correct, this is a dup of 104633. Marking as such. *** This bug has been marked as a duplicate of 104633 *** An errata has been issued which should help the problem described in this bug report. This report is therefore being closed with a resolution of ERRATA. For more information on the solution and/or where to find the updated files, please follow the link below. You may reopen this bug report if the solution does not work for you. http://rhn.redhat.com/errata/RHSA-2004-188.html |