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.

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