diskless alphalinux nodes

Robert G. Brown rgb at phy.duke.edu
Tue Jun 6 12:08:18 PDT 2000

On Tue, 6 Jun 2000, Mathew Lee wrote:

> ....additionally I searched the archives for diskless and found a reference from
> Oct. 1998, where you talk about a diskless booting sequence ...I have attached it
> to refresh your memory.  I was wondering if the diskless.tar.gz is still available,
> and/or if it has been updated.....also, is there a place that I could find
> additional information on diskless booting...mounting root-nfs or by other
> means....(ramdisk or coda possibly)

I largely abandoned this particular approach because new kernels came
out that supported much better methods.  The most intriguing is Greg
Warnes NFS hack that permits the normal installation of just one server
to support N nodes without creating any host-specific export directories
at all -- I think he posted it last week.  However, I believe that there
are other packages out there as well.

There are three different levels of problems to solve setting up and
running diskless systems.  The first is getting a kernel to load (via
the net with special proms on a NIC or from a boot floppy).  The second
is getting the kernel you boot to NFS mount your root (and other) file
system(s).  The third is efficiently laying out exports on a server so
that you provide writeability where a given system really has to have
it.  Pretty much all unixoid systems will be unhappy unless they can
write /var, /tmp, /etc and /dev, although one can often rig /etc with
symlinks to writeable space in e.g. /var/etc to fake it.  

Greg's NFS hack allows a single fs to be exported but gives writability
and remapped identity to files via an IP-based tag, so e.g.
/etc/ld.so.cache as mounted on host xxxxxxxx is really exported as
/etc/ld.so.cache_xxxxxxxx on the server.  IIRC, that is (he may correct
me).  I'd expect that his changes are moderately portable since they are
likely well above the machine hardware layer of the kernel.

However, once you've figured out how to build a NFS lilo boot floppy
(which isn't that difficult from the current howtos and e.g. mkinitrd)
it is also pretty simple to go diskless by just giving each node e.g.
/exports/[b1,b2,b3...] exported to each host as its root and then
cloning everything BUT /usr into it (that is, make /usr a separate
filesystem on the server, usually, and export it RO to all the hosts).
This wastes a bit of space but space is cheap.  You'll still need to
periodically rsync the node roots with a carefully determined exclusion
list, as otherwise e.g. RPM installs on the server won't properly
propagate to the nodes.

I might tackle an NFS/diskless installation again one day, but if I do
I'm almost certainly going to work from Greg's or one of the others that
have been posted/advertised on the list in the last few months.  Use the
search engine to find them.


Robert G. Brown	                       http://www.phy.duke.edu/~rgb/
Duke University Dept. of Physics, Box 90305
Durham, N.C. 27708-0305
Phone: 1-919-660-2567  Fax: 919-660-2525     email:rgb at phy.duke.edu

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