Ram disks

[edhall at rand-unix]

						      You probably do
    not want them to extend virtual memory (paging/swapping).  We do get
    close to the same performance (I think) by utilizing paging/swapping
    area on disks that are isolated from the rest of our system I/O.
    Most of the 11/70's swap on RK05's that have their own controller (the
    additional drives on this controller are seldom used).

Whoa!!  I thought that swapping is best done on your FASTEST disks.
An RK05 is SLOW, no matter whether it is exclusively used for swapping
or not.

I once experimented with this on a PDP-11/45 running V7 by moving
swapping from an AMPEX-980 (with a one-of-a-kind controller) to an
RK05.  Even though the AMPEX supported all filesystems as well as
usually serving as swap, moving swap off to the RK05 slowed things
down considerably; I immediately received a barrage of complaints as
to how the already slow system had gotten much slower.

Admittedly, an 11/70 with large memory is not going to be swapping
as much as this 11/45 was.  But speeding up the swapping process can
be quite significant on a system that needs to swap.  And on a paging
system, disk I/O speed can be even more important.  How a `ram disk'
is best used depends upon the system and what it is used for.

		-Ed Hall
		edhall at rand-unix
		{ucbvax,decvax}!trw-unix!randvax!edhall