linux-kernel - Re: 3ware 9650SE-4PML RAID-1 Question: One reader process starves I/O to the rest of the system?

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Date:	Fri, 16 Oct 2009 15:36:13 -0700
From:	adam radford <aradford@...il.com>
To:	Justin Piszcz <jpiszcz@...idpixels.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: 3ware 9650SE-4PML RAID-1 Question: One reader process starves I/O 
	to the rest of the system?

Justin,

Can you try turning down the queue depth of the disk that is getting
written to to see if that resolves your responsiveness issue?

I.E.:     echo "16" > /sys/block/sdX/device/queue_depth

(replace X with disk letter of device from /raid6 mountpoint).

FYI:   It's probably better to send questions like this to linux-scsi rather
         than linux-kernel.

-Adam

On Fri, Oct 16, 2009 at 2:46 PM, Justin Piszcz <jpiszcz@...idpixels.com> wrote:
> Hello,
>
> I tried CFQ/deadline schedulers, when I run the following:
>
> # /usr/bin/time dd if=/dev/sdb2 of=/raid6/sdb2.img
>
> Behind which are 2 x Raptor 150GB disks, the system is pretty much unusable
> when I control-c the dd, it comes back to life.
>
> The RAID-6 is a 15-disk RAID-6 which does 600-700MB/s writes.
>
> All cards are on PCI-e and have adequate bandwidth on a P55 board (DP55KG).
>
> Are there any recommended tuning options for a RAID-1 configuration, such
> that
> a heavy I/O read or write operation does not pause the system?
>
> During the dd..
>
> Drive Performance Monitor Configuration for /c1 ...
> Performance Monitor: ON
> Version: 1
> Max commands for averaging: 100
> Max latency commands to save: 10
> Requested data: Instantaneous Drive Statistics
>
>                               Queue           Xfer         Resp
> Port   Status           Unit   Depth   IOPs    Rate(MB/s)   Time(ms)
> ------------------------------------------------------------------------
> p0     OK               u0     25      762     26.219       19 p1     OK
>           u0     23      780     25.953       24 p2     OK               u1
>     1       0       0.000        98 p3     NOT-PRESENT      -      -       -
>       -            -
>
> Justin.
>
>
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