Scyld and fstab for Diskless slaves

[Donald Becker]

On Tue, 19 Dec 2000, Chip Coldwell wrote:

> I know how to compile a kernel to NFS mount a root filesystem, and I
> have set up diskless clusters using this method; I'm very curious how
> the ramdisk root filesystem works.  Does the node tftp down a
> compressed filesystem image and load it into the ramdisk analogously
> to the root floppies of yore, except coming over tftp instead of from
> a floppy?

Yes, that's roughly the idea.

We avoid TFTP where possible because of our experience with performance
problems and unreliability with TFTP on larger cluster.  The network is
pretty busy when all of the compute nodes are booted at once.  A simple
non-windowed protocol with short timeouts and without congestion control can
lose badly.  There is a reason that TFTP isn't used over the Internet :->.

Multicast-TFTP potentially solves the problem, and you might see that
introduced for PXE boots on large clusters.

>  Does this require custom kernel modifications, or is it a
> functionality available in stock kernels?

> On Fri, 15 Dec 2000, Daniel Ridge wrote:
> > Also, while we set up a beefy ramdisk during boot -- this space is
> > reclaimed when the node finishes booting if you aren't doing a ramdisk
> > root.
...
> > Our upcoming contains a lot of effort directed towards reducing the size
> > of ramdisk. This is to make the system work on smaller memory machines
...
> > Because we can now do this, I expect that the next version of our product
> > will ship with ramdisk root as the default.

Donald Becker				becker at scyld.com
Scyld Computing Corporation		http://www.scyld.com
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993