cestluk at polyu.edu.hk
Tue Dec 5 19:56:45 PST 2000
Donald Becker wrote:
> A common misperception when people first see the Scyld Beowulf system is
> that it is based on a NFS root scheme.
> Using a NFS root has several problems:
> NFS is very slow
> NFS is unreliable
> NFS file caching has consistency and semantic problems.
> Instead our model is based on a ramdisk root and cache, along with using
> 'bproc' to migrate processes from a master node.
> All of the NFS problems are magnified and multiplied when working on a
> Beowulf cluster. Unlike a workstation network, where users are idle on
> average and working on different jobs, a cluster is all about hot spots.
> The NFS server quickly becomes a major serialization point. (The same
> observation is true of a NIS/Yellow-Pages server: when starting a cluster
> job, every processor will try to scan the password list at the same time.)
> While a ramdisk root initially sounds like a waste of memory, the semantics
> of a ramdisk fits very well with what we are doing. The Linux ramdisk code
> is unified with the buffer cache, rather than a separate page cache. The
> files cached in the root ramdisk are mostly contain hot pages on a running
> system: the "/", /etc, /lib and /dev directories, and the common libraries.
I'd like to learn more:
1. Does that mean that the scyld slave nodes can be started without any
HD/NFS mounted root filesystem at all? And that's by all of the slave
2. What exactly are mounted in this root ramdisk? Is there any
documentation that I can refer to?
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