NetBSD Bob wrote:

> What conditions or speed advantage are gained by using mfs vs no mfs?

Things like compilers that use /tmp for temporary files see a gain
because you don't have to write the temporary files out to disk.
Softdeps will make this a little better, but using a mfs for /tmp can
be a big win.  Because it's memory based, as soon as the mfs process
controlling the filesystem disappears the data is lost.

> Where is using mfs most useful and where is it least useful?

In a nutshell - it's useful where do don't need to keep anything across
a reboot :-)  Also, size is a consideration (as others have mentioned).
I tend to try to limit my mfs's to half of physical RAM unless that RAM
is quite small (eg, I've got a 20MB mfs on a box with 32MB of RAM).

Simon.