"Spencer" <spencerp_at_swbell.net> wrote in message
news:i0P96.5432$hD5.87989_at_nnrp1.sbc.net...
> jonathon and connor have both already hit the (proverbial)
> nail on the head. and, at a risk of delivering a glancing
> blow and bending it over sideways... here's my swing at it
>
> assuming an oracle block size of 4K
>
> the odds that a single multiblock read of 16 blocks (64K)
> will require i/o operation on more than one device are:
>
> 1 in 2 given a stripe size of 128K
> 15 in 16 given a stripe size of 64K
> 1 in 1 given a stripe size of 32K
>
> the odds that a single multiblock read of 8 blocks (32K)
> will require i/o operations on more than one device are:
>
> 1 in 4 given a stripe size of 128K
> 1 in 2 given a stripe size of 64K
> 7 in 8 given a stripe size of 32K
>
> the odds that a single multiblock read will require more
> than one i/o operation on a single device are:
>
> 1 in 1 if request size > stripe size * no.of disks
> 0 if request size <= stripe size * no.of disks
>
> the odds that multiple i/o operations against a single
> device will be combined together into a single larger
> i/o operation (e.g. by async or list io) are:
>
> dependent on factors in addition to stripe size.
>
> the odds that a block will already be in the buffer cache
> and not require any i/o operation are:
>
> dependent on factors other than stripe size.
>
> does anyone care to place a wager ?
>
> "Jonathan Lewis" <jonathan_at_jlcomp.demon.co.uk> wrote in message
> news:979814882.27443.0.nnrp-02.9e984b29_at_news.demon.co.uk...
> >
> > More particularly, you do not want a single multiblock read
> > to be larger than the amount of data that can be found on a
> > single disk (unless the system is a single user system) otherwise
> > a single Oracle read request ends up queuing and blocking on more
> > than one device.
> >
> > --
> > Jonathan Lewis
> > Yet another Oracle-related web site: http://www.jlcomp.demon.co.uk
> >
> > Practical Oracle 8i: Building Efficient Databases
> >
> > Publishers: Addison-Wesley
> > See a first review at:
> > http://www.ixora.com.au/resources/index.htm#practical_8i
> > More reviews at: http://www.jlcomp.demon.co.uk/book_rev.html
> >
> > Connor McDonald wrote in message <3A643625.979_at_yahoo.com>...
> > >thus smaller stripe sizes could perform better - but as you said, you
> > >would not want a single multblock read to be larger than no. disks *
> > >stripe size since you would get nasty 'wraparound'.
> > >
> >
>
>
>
Received on Fri Jan 19 2001 - 08:16:59 CST
