On Tuesday, 11 December 2001 at 23:41:51 +0100, Wilko Bulte wrote:
> 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.

That's what Vinum does.

> 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.

Yes, that's reasonable.

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

I don't think that UFS would behave that differently, just faster :-)

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