gstripe performance scaling with many disks

[R. B. Riddick]

I found this
  static intmax_t default_stripesize = 4096;
in
  src/sbin/geom/class/stripe/geom_stripe.c

The stripe-fast feature will help less and less (just as Ivan described it). A
solution would be to increase stripe size to something bigger (like 64KB), so
that always two drives r busy (128KB/64KB), but then u would not see speeds
higher than 2 times single-drive-speed, because dd does not read ahead on a raw
device (UFS would possibly).

You could try your own "dd", that issues 20 read requests nearly at the same
time, so that this 128KB limitations does not have an impact...

Or u could try raidtest (from ports), which can already do multiple
simultaneous requests (but random read and not sequential read; but ur read
performance is not limited by the disk but by ipfw, IIRC)...

gcache certainly would do some read-ahead, too...

-Arne



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