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Re: OT: high WIO on Linux

From: Nuno Souto <dbvision_at_iinet.net.au>
Date: Wed, 15 Mar 2006 21:12:17 +1100
Message-ID: <4417E881.5090900@iinet.net.au>


Mark Brinsmead wrote,on my timestamp of 15/03/2006 3:25 PM:
> Kevin,
>
> A good observation. And one with which I agree.
>
> Are the depths of my I/O queues in any way "tunable" under Linux?
> (I'm pretty sure I recall tuning this under AIX...) I would expect that
> Linux will make some rather bland assumptions about the SCSI or FC
> "disks" it finds in my (hypothetical) RAID-array. Or is it smart enough
> to query the device in the hope of learning the best queue depth to
> use... (I have no doubt that the SCSI standards permit such queries,
> but that does not necessarily mean that the OS will bother to ask, nor
> that the device will provide a "truthful" answer.) Anyway, I would
> expect a RAID-array with a few GB of NVRAM to be able to support queue
> depths into the tens of thousands. Is that irrational?

Some of the device drivers - megaraid is one of them - will allow you to set the io queue depth, set to default of 64 requests in most cases with RH4. Not the best of solutions as it becomes hardware supplier or device driver dependent. But better than nothing, I suppose... I'd much rather it was the same way AIX does: controlled by the OS and then the device driver can apply its own optimal value if and when needed.

-- 
Cheers
Nuno Souto
in sunny Sydney, Australia
dbvision_at_iinet.net.au
--
http://www.freelists.org/webpage/oracle-l
Received on Wed Mar 15 2006 - 04:12:17 CST

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