Re: How to setup SWAP partition for diskless client

[Ben Kressman <bkressman@netexplorer.com>]

Dan Shearer wrote:

> > > > > 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

  Well, in my experience, try to get a 4 meg machine up and running as a linux
workstation without a nfs swap is impossible.

-Ben