Scyld and fstab for Diskless slaves

Chip Coldwell coldwell at frank.harvard.edu
Tue Dec 19 10:57:00 EST 2000


Interesting, so what is the mechanism for transmitting the compressed
root filesystem image to the node, if not tftp?  I suppose you could
configure the kernel to mount an NFS filesystem, retrieve a compressed
filesystem image from it, expand it into a ramdisk, and then remount
the result as /, but that's pretty kludgey.

BTW, if I'm getting close to any of Scyld Computing's IP it's not
because I want to avoid buying something from you ... it's just that I
want to make sure that the cluster I spec will work with your
software.  In particular, I'm planning to spec nodes that have no
local persistant storae whatsoever, i.e. no hard disk, no floppy and
no cd-rom (the less there is, the less there is to go wrong).  I know
this configuration will work with my NFS-root diskless configuration
because I've done it, but I like your ramdisk system better when the
network is the bottleneck (and mine better when memory is ...).

Thanks for the prompt reply,

Chip

-- 
Charles M. "Chip" Coldwell
"Turn on, log in, tune out"

On Tue, 19 Dec 2000, Donald Becker wrote:

> 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
> 


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