Date: Wed, 6 Jan 1999 00:49:41 -0500 (EST) From: Brian Dean <brdean@unx.sas.com> To: freebsd-current@FreeBSD.ORG Subject: Filesystem overflow ... can it be done? Message-ID: <199901060549.AAA20034@dean.pc.sas.com>
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Hi,
Once a filesystem fills up, is there a way to have it "overflow" into
another filesystem or area of storage?
I want build a machine whose filesystem is memory-base, i.e.,
MFS_ROOT, where root, usr, var, etc, etc, is all memory based.
However, I expect a goodly amount of temporary data to have to be
dealt with in /tmp, but not all of the time. The primary reason for
this is for fast data and program access. The machine could be booted
with a BOOTP kernel, and everything downloaded into it's MFS when it
comes up.
The problem is that /tmp can fill up at peak times, because I can't
put enough RAM in the machine to cover the expected maximum. I would
be willing to lose performance in this case by having my /tmp overflow
onto disk-based storage when necessary, but I wouldn't want to use
disk storage all the time.
For a long time now, I've used /tmp as a memory based filesystem, and
the rest of the OS on disk with good performance results. I'd like to
experiment with putting more of my heavily hit code into MFS and maybe
take this to the extreme end of the spectrum of having everything in
MFS, while still leaving enough RAM to run my processes.
Some of my questions are:
1) Can nearly the same results be achieved by dedicating large
amounts of memory for disk buffers?
2) I don't like the idea of consuming RAM with programs in the
MFS, only to get loaded into RAM again to be executed.
Gzipping my executables will help, however, this will
increase the activation time, and I don't want to go to all
this work to have performance lost by decompression. Maybe
the answer to this would be covered in part by the first
question?
3) Is this even doable with the filesystem technology in
FreeBSD? A while back I remember discussions about
stackable filesystems which I think might be relevant
here.
Thanks for any help and suggestions.
-Brian
--
Brian Dean Process Engineering brdean@unx.sas.com (x5235)
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