ram disc

[David Houlder]

Folks...

My experience with Solaris (and maybe SunOS 4.x?) is this.  You can
specify a file system type of "tmpfs" in the mount command (or
/etc/[v]fstab) and it will use the virtual memory space. See man tmpfs,
man mount_tmpfs. This is how /tmp is normally done.

If you have lots of memory, then you essentially have a ram disc. If
you don't, then you get more paging and you might as well have made it
a disc filesystem to start with.

I imagine that a unix that offers some sort of memory-based filesystem
does it this way.

> Excuse me if I'm being a bit slow-witted, and God help me if I draw the
> flame attention THIS thread has recently generated, but...

What! You're not committing the unpardonable sin of admitting that you
may not be a walking unix encyclopaedia, are you?  Your pop-up toaster
probably doesn't even have a SCSI bus... :-)


> ... wouldn't a
> "true" RAM disk run counter to the UNIX file system sharing
> philosophy?  Since all file systems are owned by someone, with strict
> permission testing, wouldn't the creation of a file system in RAM
> simply wall off that portion of RAM from other users?

My understanding is, yep, thats what happens, except that because its
virtual memory the situation is not quite that drastic: with any luck
your "filesystem" will be swapped out most of the time and the rest of
the users will get about as much real memory as they would without
tmpfs. 


> There is still the problem of needing to
> have root access in order to mount file-systems, as well

Unfortunately, yes.

> Just my thoughts-- not meant to draw fire....
None drawn.


David Houlder                           Phone:  +61 6 249 4613
Geography Department                (In Aust.:  (06) 249 4613)
The Australian National University        Fax:  +61 6 249 3770
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