[Beowulf] motherboards for diskless nodes

Greg Lindahl lindahl at pathscale.com
Fri Feb 25 13:31:46 EST 2005


On Fri, Feb 25, 2005 at 06:52:59PM +0100, Ryan Sweet wrote:

> While I can understand debating over the merits of nfsroot vs RAM-disk 
> root, I fail to see many useful arguments for maintaining a local OS 
> install.

An example of something that goes very wrong with NFS is upgrading a
file to a new file with the same name. If that file is a binary or
library that's in use anywhere in the cluster, you are likely to have
a problem. Local disks and Scyld, on the other hand, do the right
thing: existing processes using the binary or library continue to use
the old version, while new ones use the new version.

This disagreement is as old as the hills, by the way: in the good old
days, when Sun was young, lots of people ran their pizza-box
workstations diskless, but that went out of style when Ethernet's
performance was stuck in place for a bunch of years.

It's important to understand arguments you disagree with; your
dismissal is not a good sign.

> It can be _very_ useful in a situation where you have to support multiple 
> user communities with wierd apps or strange requirements.

Yep. But your conclusion:

> That sort of config requires 
> a lot of glue, but it would be way too much headache to even attempt 
> without "diskless" systems.

Doesn't make any sense; I have seen people describe such systems where
they download a disk image when a batch job wants a different software
load. It's certainly doable that way: it does have different tradeoffs
from the diskless case, but if it gives you a headache, it's probably
because you don't like it, not because it's hard to do.

-- greg

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