DN8500C on Ultra2 buffer size in st_options.h

     With the default 32 1k block buffer in options.h, an Ultra2 will not
stream a DN8500C drive, it only gets about 500k/s most of the time.

     If I increase the buffer size to 256k, it writes wonderfully, streams the
drive and gets a thruput of around 1100k/s, which given it's on a narrow SCSI
is about as good as it will get.

     I've got one of the combo 10-base-T/narrow SCSI s-bus cards to which this
drive is connected.

     If I increase the buffer, while it makes the writes work wonderfully, an
attempt to read a tape results in a kernel panic, it seems to be pretty random
but TL1: local_irq_count shows up a lot.

     If I only increase it to 64k (which isn't adequate to stream the tape),
it doesn't panic the kernel when I attempt to read but all attempts at reading
tapes result in errors as if the media were bad, but go back to 32k and it
reads again.

     I'm hoping someone can enlighten me as to why jacking the size of the
buffer up causes problems on the Ultra2.  I've read about people with Intel
boxes doing it to good effect.



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