Ram disks

[ron at brl-bmd]

From:      Ron Natalie <ron at brl-bmd>

The PDP 11/70 systems I described already had maximum memory, and we
have block buffers, inodes, and clists buffered outside the kernel
address space.  What we were looking for was some extra performance
under some previously unturned stone.

If you are going to use RAM disk for paging/swap, byte for byte pairing
it with more main memory probably show that RAM disk is not the way to
go.  I spent a lot of time at Martin Marietta convincing people that
RAM disk was not main memory.  Using it to buffer large common images
(RSX-11) was not the way to go.  It becomes of use when you are using
data that must be stored in disk form.  Some of our database key files
for that application and as I described, popular UNIX directories for
our current application are what you want these for.  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).  The VAX's
are configured so that paging space is on different drives or controllers
if that is possible from the most active file systems.

-Ron