Re: How to setup SWAP partition for diskless client

[Dan Shearer <dshearer@spri.levels.unisa.edu.au>]

> > > > How do I set up the SWAP partition for a Linux diskless client using a Linux
> > > > server's diskspace?  Thanks.
> > > 
> > > Swapping on an nfs drive is a bad idea. Usually the best thing to do is 
> > > not have a swap partition at all.
> > > 
> > And what if your memory runs out?
> 
> I think the same thing as if swap runs out, your mallocs fail until space 
> becomes available, nothing serious.

Yep. But as Paul said, memory is the key. Applications load pages on demand
so if you have less memory available you may have to request pages more 
frequently.

But think about it, what is the difference between:

	- requesting a page, getting a fault and having it loaded in
	  from swapfile over the network, and

	- requesting a page, its not there and so it is loaded from the
	  filesystem over the network

in the first case there is the overhead of having a swapfile at all, and 
it involves copying the same information twice over the network instead 
of once. This is where you can achieve significant reductions in network 
traffic by _not_ using a network swap.

You need a network swap if you think that you are going to approach the 
limiting case where your data pages are going to be more than can be held 
in memory, even when all possible discardable pages have gone.

> I would have thought the best way to set up a diskless box was to swap 
> over NFS, but to add RAM to the box so that the swap is hardly ever used.

This is a good solution except where you have a lot of clients who are 
all likely to run out of resources at once, for example at an educational 
institution. In this case they all start swapping to the network at once!

There is also a similar argument to the one that lead to the invention of
token ring after ethernet became popular: if you don't have a swap you can
never get flooded by network swapping, if you do but it isn't used much
you can never be 100% sure that you won't have a flood. 

Dan