How to make 4.2BSD ``/etc/dumps faster

[Chris Torek]

I didn't like the pipes idea, so I wrote a ``mass driver'' device
driver that runs other raw devices through their block interface.
It manages to keep even the TU78 busy most of the time (125 ips at
6250 bpi, or 781K/sec) when run off Eagle disks in single user mode.

I figured pipes would be fairly slow 'cause the network interface
limits you to 2048 bytes per transfer (although you can increase
it).  This means that for a 10240 block write (like dump() uses)
you need 5 pairs of context switches, which can beat a 750 into
the ground pretty well.  Also, it makes it harder to communicate
success/failure statuses.

Chris