Re: Memory file systems

[Chris Ross <cross+netbsd%distal.com@localhost>]

On Feb 10, 2010, at 16:40, Simon Burge wrote:
> Chris Ross wrote:
> >   My basic question is, why are there both mfs and tmpfs, what are
> > the pro's and con's of each, and which (if either) is likely to
> > receive more support/attention in the future?
>
> One area is the size of the metadata needed to represent a file in
> memory.  mfs needs just a directory entry and an inode, whereas tmpfs
> needs a couple of different UVM objects.  I don't recall the exact
> details, but it was something in the order of 2-3 times more memory
> was required by tmpfs for metadata.  This has implications for any
> memory file system where need a large number of files - say a cvs
> temp directory.
>
> I can dig up some (oldish) data if you want more info.

  This is interesting.  So, in my [casual] use, I guess this could
affect two things in two or more ways.  In the case of a slow, lightly
used, small RAM system, what you mention above sounds like mfs might
be better.  On a higher-powered machine, with more RAM, it would be
less of an issue.  Would tmpfs be higher-performance?  More efficient,
at least based on the reason for tmpfs' creation, right?

  In my case, these are both being looked at as candidates for the
machines regular /tmp.  I've always been fond of the idea of /tmp
being "gone" at reboot, and as fast as possible.  Would either tmpfs
or mfs be better for this, in general, or are there too many
pluses and minuses of each to say anything so general?

              - Chris