Re: Memory file systems

[Simon Burge <simonb%NetBSD.org@localhost>]

Chris Ross wrote:

>    Quite some time ago, I remember there being a conversation about  
> the pro's and con's of mfs vs. tmpfs.  There may, for all I've  
> tracked, be further "fast non-durable file system" options now-a-days.
> 
>    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.

Cheers,
Simon.