ram disc

David Houlder david at dart.anu.edu.au
Tue Jul 4 08:00:00 EDT 1995


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

> 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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