Just depends on your settings...
eg max phys io = 1m, db mult read * blk size = 1m
then
- 64k stripe means 16 disks in the read
- 128k means 8
- 512k means 2
- 1m means 1
etc
Involving lots of disks in a single read tends be good
for systems will small user populations (basically
you're better at a given point in time there will only
be 1 or 2 concurrent queries on the system and you
still want to maximise IO bandwidth). As the user
population gets larger, then involving lots of disks
in a single read can often lead to IO "thrashing"
Cheers
Connor
- Jared Still <jkstill_at_cybcon.com> wrote: >
> 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
> > --
> > Author: Post, Ethan
> > INET: Ethan.Post_at_ps.net
> >
> > Fat City Network Services -- 858-538-5051
> http://www.fatcity.com
> > San Diego, California -- Mailing list and
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> >
>
> > To REMOVE yourself from this mailing list, send an
> E-Mail message
> > to: ListGuru_at_fatcity.com (note EXACT spelling of
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> > the message BODY, include a line containing: UNSUB
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> --
> Please see the official ORACLE-L FAQ:
> http://www.orafaq.com
> --
> Author: Jared Still
> INET: jkstill_at_cybcon.com
>
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Connor McDonald
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Received on Mon Nov 25 2002 - 03:54:01 CST
