On Sun, 2013-02-03 at 04:07 +0600, Roman Mamedov wrote:
> On Sat, 02 Feb 2013 15:52:12 -0600
> Stan Hoeppner <stan@xxxxxxxxxxxxxxxxx> wrote:
>
> > So under heavy read load, in this case we'd probably want the slow 3TB drive
> > to contribute to the workload.
>
> No, it should behave as documented.
>
> -W, --write-mostly
> subsequent devices listed in a --build, --create, or --add com‐
> mand will be flagged as 'write-mostly'. This is valid for RAID1
> only and means that the 'md' driver will avoid reading from
> these devices if at all possible.
^^^^^^^^^^^^^^^^^^^
I would assume that if the kernel thinks the SSD is starved for io (that
being the %util column in iostat) it would consider sending io to the
HDD. At least that would be what I would expect to happen, so if the SSD
reports wrong utilization numbers back or anything else involved in the
io processing the the behavior is as expected.
>
>
> if at all possible = if there is any other mirror still alive, do not read from
> this one.
>
> BTW I also run an SSD+HDD array, and after a brief testing today I did notice
> some reads from the HDD on reading from the array showing up in iostat. So I
> can confirm the bug.
>
/Tommy
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