Re: Is Read speed faster when 1 disk is failed on raid5 ?

[Jakob Oestergaard <jakob@unthought.net>]

On Mon, Oct 28, 2002 at 10:27:46AM -0800, Yiqiang Ding wrote:
> I had the similar result with IDE drives through hpt374 controller. Still
> don't understand why a degraded system has better read performance.

Could you comment on the guesses I made below, relating to the chunk
size?

> > Other than that... Well, if the parity information is intact, the disks
> > would need to skip the parity blocks when the array is read from
> > sequentially.  With a degraded array, the reads are all contiguous on
> > the disks - this could be a difference perhaps??
> >
> > What chunk size are you using?  And can you try a chunk size that is an
> > order of magnitude bigger or smaller?   (might take some time to test
> > this out).
> >
> > For example, if you use a 4k chunksize (I don't think you do, if my last
> > guess holds), then try 128k.  If you are using 64k or above (which,
> > again, if I am guessing correctly, is probably more like what you're
> > using), then try 4k.

-- 
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