"swap" partition leads to instability?

Polytropon freebsd at edvax.de
Sun May 26 09:32:36 UTC 2013

On Sun, 26 May 2013 16:09:06 +0700, Erich Dollansky wrote:
> Hi,
> On Sun, 26 May 2013 01:58:32 -0700 (PDT)
> "M. V." <bored_to_death85 at yahoo.com> wrote:
> > I have a 24/7 network server/gateway with FreeBSD-8.2 on a SSD drive.
> > it's partitioned as normal (/ , /tmp, /var , /usr and swap) for a
> > long time now. But recently I heard from a FreeBSD expert that I
> > shouldn't have swap partition for my server, and having swap
> > partition could make my server unstable. this was so strange for me,
> > and I searched a lot but couldn't find a reason for this claim.
> > 
> because it is a false claim. I never ever have had any system with
> working hard, that gave a problem because of the swap space.

I think the "problem" here is that he's using a SSD.
As soon as the swap partition is being in heavy use,
which means it receives many writes, this may lead
to the SSD "wearing out", decreasing its lifetime.

Swap space usually does not make a system unstable.
Sometimes, the opposite is true. :-)

So if you're using a SSD, you can apply certain
optimizations to increase its lifetime so it can be
in use for several years (running 24/7). Here are
some suggestions -- check if they are useful in your
specific case!

# newfs -m 0 -i 16384 -b 16384 -f 2048 -U /dev/ada0a

This assumes that you don't have created any
slices, just one bootable partition covering the
whole disk (therefor ada0a).

Create a swapfile like this:

# /bin/rm -f /swapfile.tmp
# /bin/dd if=/dev/zero of=/swapfile.tmp bs=16m seek=1k count=0
# /sbin/mdconfig -a -t vnode -u 0 -f /swapfile.tmp || /bin/sh
# /bin/chflags nodump /swapfile.tmp
# /bin/rm -f /swapfile.tmp
# /sbin/swapctl -a /dev/md0

This makes the system use a "disk-backed dynamic
swap file". If the swap won't be used, no space will
be occupied or "reserved" on the SSD.

You can also think about "changing stuff" you won't
need to store on the SSD, maybe some content of /tmp
or /var. You can also put those into a "memory disk".

The "SSD rule" is: Minimize writes if you can. This is
a _general_ rule and does not correspond to swap only!

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

More information about the freebsd-questions mailing list