Re: raw/block device disc troughput

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> It seems that I have to update my understanding of raw and block
> devices for discs.  [...performance oddities...]

Mostly I have nothing useful to say here.  But...

> 2. I would have expected inceasing the block size above MAXPHYS not
>    improving the performance.

There is at least one aspect of performance that will not be cut off by
MAXPHYS, that being syscall overhead.  I don't know your system (you
don't say which port you're running on, for example), but if syscall
overhead for your hardware is not ignorably small compared to the costs
of doing the disk transfer, then doing one syscall per 256K will be
four times as costly in syscall overhead as doing one syscall per 1M,
even if it is four times as costly in disk transfers.

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