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

[William Warren]

On 2/9/2011 4:47 AM, Matthias Saou wrote:
> Hi,
>
> I just got this isolated RHEL6 server, with hardware I've never used
> before. It's a Supermicro X8STi motherboard (Xeon i7 920) with two cheap
> SATA disks (WD10EADS-00P8B0) using software RAID-1.
>
> The system is unusable : A quick strace of various processes shows very
> long waits during many different I/O related calls such as open, read,
> pread, stat, fdatasync...
>
> I've tried failing every other partition in order to be sure to use only
> one disk for a while, with the same results. Running RAID rebuilds
> sometimes peaks at 60-100MB/s but very rarely. Right now for instance,
> the main 900GB RAID-1 is rebuilding from sda2 to sdb2 and it's
> reporting 400kB/s with system load of over 2 (the server is idle apart
> from this rebuild). While this is going on, even smartctl on sdb takes
> time to respond. When no rebuild is in progress, the problems are the
> same.
>
> I'm using the latest released 2.6.32-71.14.1.el6.x86_64 kernel, and
> here is the detail of the SATA controller(s) :
>
> 00:1f.2 IDE interface: Intel Corporation 82801JI (ICH10 Family) 4 port
> SATA IDE Controller #1 Subsystem: Super Micro Computer Inc Device 0009
> 	Kernel driver in use: ata_piix
> 	Kernel modules: ata_generic, pata_acpi, ata_piix
> 00:1f.5 IDE interface: Intel Corporation 82801JI (ICH10 Family) 2 port
> SATA IDE Controller #2 Subsystem: Super Micro Computer Inc Device 0009
> 	Kernel driver in use: ata_piix
> 	Kernel modules: ata_generic, pata_acpi, ata_piix
>
> No errors reported by the kernel apart from some processes stuck for
> more than 120s before the last reboot. Has anyone seen disk I/O issues
> like this with RHEL6 and similar hardware?
>
> Matthias
>
> PS: A possibly important detail is that this is a server provided by
> ovh.com which has been offering RHEL6 for a while but still has it
> marked as "BETA" (it's not the RHEL6 beta, it's how they consider their
> offering of RHEL6), which might indicate known problems between their
> typical hardware and RHEL6. I didn't find any clues with a quick
> bugzilla search...
>
are you using the bios raid or MD raid?  If you are using biod raid you 
are running everything effectively pio mode and it's going to suck.  Put 
the bios in ahci(not raid mode) and then use Linux raid from inside the 
partitioning scheme(which is md raid) i bet performance will be much better.