Re: software raid issues -- possible kernel I/O problem?

Jakob Østergaard (jakob@unthought.net)
Sun, 9 Dec 2001 20:19:00 +0100

On Fri, Dec 07, 2001 at 05:39:53PM -0500, Chris Friesen wrote:
>
> A number of people have privately pointed out that hdparm -T doesn't
> actually go to the disk at all. Guess I should RTFM...I though that
> this was reading from the disk's cache, not linux's cache. Oops.
>
> I'm still kind of curious why raid-1 reads don't seem to get any
> performance increase over reads from a single disk. Any ideas?

For one single large sequential read, the current RAID-1 code will
not show any significant benefit over the single-disk case.

However, if you read many smaller files, or have multiple concurrent
readers, you should see a good speedup.

Try running two bonnies at the same time.

-- 
................................................................
:   jakob@unthought.net   : And I see the elder races,         :
:.........................: putrid forms of man                :
:   Jakob Østergaard      : See him rise and claim the earth,  :
:        OZ9ABN           : his downfall is at hand.           :
:.........................:............{Konkhra}...............:
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/