[rhelv6-list] Performance issues with RHEL6 (iowait)

[Matthias Saou]

Manuel Wolfshant wrote :

> Can you please check that the drives are seen by the system via the SCSI 
> ( as opposed to older PATA ) protocol ? The BIOS must be configured to 
> avoid legacy/compatible mode by all means ( and use AHCI instead )

I'm guessing you're referring to a problem I've indeed seen on some
similar hardware which had 82801I (ICH9 Family) and where the default I
saw with RHEL5 was indeed to have the SATA drives appear as hda and hdc
and resulted in very poor performance. That problem is solved by
passing hda=noprobe and hdc=noprobe to the kernel. It's not what I'm
seeing now, where both disks are sda and sdb, and the problem isn't
that all disk transfers are slow, it's that I/O calls seem to stall
very often for multiple seconds.

Right now, the RAID-1 rebuild from sda2 to sdb2 is at 40MB/s sustained
with all 8 CPUs (Quad HT) at 0.0% wait and a load of 1. This is what I
would expect from an idle system. But moments ago, and for hours, it was
nearly stalled with always at least 1 CPU at 90%+ wait and all of those
I/O pauses for everything.

I'm really confused, and still not even sure wether it's a hardware or
software problem in the first place.

Matthias

-- 
Clean custom Red Hat Linux rpm packages : http://freshrpms.net/
Fedora release 14 (Laughlin) - Linux kernel 2.6.35.10-72.fc14.x86_64
Load : 0.06 0.03 0.07