Using mdconfig for swap space

Mel Flynn mel.flynn+fbsd.questions at
Wed Sep 9 14:37:35 UTC 2009

On Wednesday 09 September 2009 15:07:37 Peter Steele wrote:
> Thanks for the responses. The reason I'm looking at doing this is that we
> have increased memory on our platform from 4GB to 8GB and therefore have to
> increase swap space from 8GB to 16GB.

No you don't. It's advised, but not mandatory.

> We have enough space in our /var
> partition that we could add a swap file there and not have to touch the
> existing partition layout. I like the simplicity of the swap file approach,
> but we have an application that is very sensitive to I/O performance and
> I'm a little wary what this could mean. QA I know would have a field day in
> trying to pound the system with all sorts of stress tests. I think a
> dedicated swap partition is probably a safer option.

Any I/O bound application suffers from any kind of swap. You would do better 
to first establish how this application suffers once you start swapping. If 
your machine needs more then or even close to 8GB of swap, I doubt the 
applications are responsive to begin with. With 8GB of memory, it's probably 
better to have 2GB of swap, so that offending applications are killed off 
sooner and the machine is able to recover sooner. But - I'm assuming this is a 
server, for a multimedia machine - editing large images or videos - more swap 
is beneficial as inactive images/videos can be swapped out.


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