Bug 183598
| Summary: | high iowaits with long transfers | ||||||
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| Product: | Red Hat Enterprise Linux 3 | Reporter: | Johan Dahl <johan.dahl> | ||||
| Component: | kernel | Assignee: | Tom Coughlan <coughlan> | ||||
| Status: | CLOSED CANTFIX | QA Contact: | Brian Brock <bbrock> | ||||
| Severity: | medium | Docs Contact: | |||||
| Priority: | medium | ||||||
| Version: | 3.0 | CC: | johan.dahl, lwoodman, petrides | ||||
| Target Milestone: | --- | ||||||
| Target Release: | --- | ||||||
| Hardware: | i386 | ||||||
| OS: | Linux | ||||||
| Whiteboard: | |||||||
| Fixed In Version: | Doc Type: | Bug Fix | |||||
| Doc Text: | Story Points: | --- | |||||
| Clone Of: | Environment: | ||||||
| Last Closed: | 2006-03-20 14:39:13 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: | |||||||
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Description
Johan Dahl
2006-03-02 07:40:54 UTC
Copying lots of smaller files is no problem. Please provide a sysreport (or at least /var/log/messages). Make sure you have the latest firmware for the ServerRaid 4Lx. I believe this controller has a battery-backed up cache, and the cache is not used if the battery is dead. So please check the ServerRaid BIOS utility for any errors. Also, let me know the firmware settings you are using for the RAID 5 (e.g. does it let you set the chunk size?). I suspect you would not have this problem with a RAID 1. Is it feasible for you to test this theory? Whan did this start happening? Was there a version of Linux where you did not have this problem? Created attachment 126077 [details]
sysreport
Sysreport provided above Going to install the latest firmware. 7.12.07 instead of 7.10.18. This means weekend work for me :-( The controller has no battery-backed up cache installed. Raid 5 settings is Strip unit size 8kb which is optimal for file/print servers. If the firmware update makes no difference should I construct a raidset with 32 or 64kb stripesize? It is a production system so I needed extra disks to test the raid 1 theory. I created a Raid 1 setup with two 146 Gb disks and tried making long copies. The iowait never got over 45% and the system remained responsive. Tested both with and without LVM but that made no difference. I am not sure I has ever worked a it should. During the first period we had a lot of network errors but some small amount of them could have been this problem. Firmware updated and problem still exists. I also updated to Update 7 and kernel 2.4.21-40.ELsmp but the problem still exists. Based on your comment #4, the problem seems specific to RAID 5 on the ServeRaid adapter. RAID 1 performs well. I am surprised this board does not have a battery backed up cache. I thought they all did. You might ask IBM whether this would solve the problem. Maybe they can also advise you about the optimal stripe size for your workload. Beyond that, you can try elvtune http://www.redhat.com/support/wpapers/redhat/ext3/tuning.html and you can try adjusting min/max-readahead: http://www.redhat.com/magazine/001nov04/features/vm/ See "Tuning the VM" I have a report that the following values helped in at least one situation: echo 8192 > /proc/sys/vm/max-readahead echo 2048 > /proc/sys/vm/min-readahead I am going to close this, since it appears to be a ServeRaid RAID 5 performance problem. Re-open it if there is more to it than that. |