Re: [Xen-users] Slow domU disk performance

["Christopher G. Stach II" <cgs@xxxxxxxxx>]

Eric Peterson wrote:
> Hi,
> 
> I am running Xen 3.0.2 on dual core Opteron with 6GB RAM.  The machine
> works fine except my guest domains have a problem when disk I/O is
> involved where they become unresponsive and top shows "100% wa" for
> cpu usage. This happens when running a larger select from a postgresql
> database.  dom0 and my other domU's remain responsive the whole time
> so it seems like it is an issue with the configuration of the domU and
> not with the hardware or underlying system.
> 
> I'm exporting the disks as SCSI devices and the the main disk is a
> SATA RAID array running of a 3ware card. I know with ATA/IDE disks you
> can use hdparm to tune the disk, but since these SATA drives are seen
> as SCSI drives that's not possible AFAIK.
> 
> Does anyone have any recommendations or places to start looking? I
> searched the list, but couldn't find a whole lot.
> 
> Thanks,
> Eric
> 
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Are you using cfq or deadline scheduler in dom0?  Is your dom0
prioritized (Xen scheduler) below the domUs?  Are you using any sort of
shared FS between the domUs?  Is the affected domU prioritized properly
for the kind of work it does?  Are you using file backed stores instead
of raw partitions (LVM, actual partitions) for the DB?

-- 
Christopher G. Stach II

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