On Wed, Dec 12, 2001 at 09:00:34AM +1030, Greg Lehey wrote:
> On Tuesday, 11 December 2001 at 15:34:37 +0100, Wilko Bulte wrote:
> > 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:
> >>>


> >>>     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.
> So what did it do with user requests which crossed stripes?

Memory is dim, but I think the fs code created a second i/o to the
driver layer. So the fs never sent out an i/o that the driver layer had
to break up. In case of a pre-fetch while reading I think the f/s 
would just pre-fetch until the stripe border and not bother sending
out a second i/o down. 

In the end all of this benchmarked quite favorably.
Note that this was 386/486 era, with the classic SysV filesystem.

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

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