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

[adam radford]

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@xxxxxxxxxxxxxxx> 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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