Re: 1M STRIPE SIZE BEST?

Maybe I've forgotten something fundamental about the way RAID 5 works, I dunno.

But I'm having a hard time understanding how stripe size is going to determine the number of heads used in an IO.

RAID 5 distributes the data across all spindles, with 1 or more of the spindles for any IO being used for the parity data.

Someone care to enlighten me?

Thanks,

Jared

On Thursday 21 November 2002 06:33, Thomas Day wrote:
> We had a discussion about a year ago here and if I remember correctly the
> "best" stripe size is a function of number of concurrent users. With a
> small number of users you want a small stripe size so that each read i/o
> will utilize the maximum number of heads. It will also tie up the RAID
> device for the duration of the read. With a large number of users you want
> a very large stripe size so that a minimum of heads will be used for each
> read and the RAID device can handle multiple requests at a time.
>
> I don't recall any specific numbers and, as you say, the technology is
> changing so quickly that a discussion from a year ago may not be pertinent
> to today's environment.
>
>
>
>
> "Post, Ethan"
> <Ethan.Post To: Multiple recipients of
> list ORACLE-L <ORACLE-L_at_fatcity.com> @ps.net> cc:
> Sent by: root Subject: 1M STRIPE SIZE BEST?
>
>
> 11/20/2002
> 05:53 PM
> Please
> respond to
> ORACLE-L
>
>
>
>
>
>
> A number of papers recommend a stripe size of 1 M (even for EMC) for
> volumes
> containing data files. I also have the following email from Eyal Aronoff
> of
> Quest dated Nov 2000. A number of the white papers are more recent.
>
> ============================================================
> The reasons for a larger stripe size on a non-RAID 5 device are:
> 1) Sequential reads are faster if you can take advantege of the read ahead
> built into the disk caching
> 2) If a 64K read does not start on the first block of the stripe, two
> "spindled" are locked for the duration of the read
>
> However, lately we have been testing some EMC gear and it looks like EMC
> have optimized both of those for smaller strip size too.
>
> The bottom line - I no longer have an opinion one way or another. The
> undelying technology just changes too rapidly.
>
> Eyal
> ============================================================
>
> Your opinions/comments as far as a "best" practice in setting stripe sizes
> would be greatly appreciated.
>
> Thanks,
> Ethan
> --
> Please see the official ORACLE-L FAQ: http://www.orafaq.com
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> Author: Post, Ethan
> INET: Ethan.Post_at_ps.net
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Author: Jared Still
  INET: jkstill_at_cybcon.com

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