>However, reading from the drive is 5-6 times slower, even though the
protocol is essentially identical except that when the actual data is
transferred it goes the other direction.
Is it possible your getting srb timeout’s, so part of the time the serial
port isn’t busy and the scsi port driver is resetting the bus? The driver
that just spins in the StartIO function never gives the port driver a
chance to timeout srb’s. You can globally change the disk srb timeout with
a registry entry.
Adjusting the maximum transfer size may also influence this. DIsk srb
timeouts I believe are normally a few seconds, so if your trying to read a
64 kbyte buffer from a 115kbps serial link, this may not happen in a few
seconds.
You might try a little test that opens the disk for unbuffered I/O and then
does read/write in increasing sizes of blocks. If there is a sudden step
down in performance you might get a good clue.
- Jan
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