On Tue, Dec 11, 2001 at 11:06:33AM +1030, Greg Lehey wrote:
> On Monday, 10 December 2001 at 10:30:04 -0800, Matthew Dillon wrote:
> >
> >>>     performance without it - for reading OR writing.  It doesn't matter
> >>>     so much for RAID{1,10},  but it matters a whole lot for something like
> >>>     RAID-5 where the difference between a spindle-synced read or write
> >>>     and a non-spindle-synched read or write can be upwards of 35%.
> >>
> >> If you have RAID5 with I/O sizes that result in full-stripe operations.
> >
> >     Well, 'more then one disk' operations anyway, for random-I/O.  Caching
> >     takes care of sequential I/O reasonably well but random-I/O goes down
> >     the drain for writes if you aren't spindle synced, no matter what
> >     the stripe size,
> Can you explain this?  I don't see it.  In FreeBSD, just about all I/O
> goes to buffer cache.
> >     and will go down the drain for reads if you cross a stripe -
> >     something that is quite common I think.
> I think this is what Mike was referring to when talking about parity
> calculation.  In any case, going across a stripe boundary is not a
> good idea, though of course it can't be avoided.  That's one of the
> arguments for large stripes.

In a former life I was involved with a HB striping product for SysVr2
that had a slightly modified filesystem that 'knew' when it was
working on a striped disk. And as it know, it avoided posting I/O s
that crossed stripes.

|   / o / /_  _                 email:  [EMAIL PROTECTED]
|/|/ / / /(  (_)  Bulte         Arnhem, The Netherlands 

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