Questions and Sanity Check

Donald Becker becker at
Fri Mar 2 08:26:40 PST 2001

On Fri, 2 Mar 2001, Jim Phillips wrote:
> On Fri, 2 Mar 2001, Donald Becker wrote:
> > 
> > The cached libraries on the slave nodes are 10-40MB uncompressed.
> > That's on the order of 1 second of Fast Ethernet time to transfer the
> > compressed version.  The boot time isn't a significant issue.
> Of course, if you reboot 64 nodes at once and they all try to download
> from the front end node at the same time, then five seconds to download
> one node turns into five minutes to start up the entire cluster.

The "initial ramdisk" (a slight misnomer) is compressed, typically 3:1.
It's transferred efficiently over TCP, not with slower NFS.
Two or three minutes to boot isn't very long compared to how long some
machines take to count 512MB of memory.  Does anyone have the number for
booting a 64 node SP/2?  I've heard some pretty horrible numbers.

> However, I agree that this isn't really significant.

A dynamic library caching system is interesting mostly for run-time
efficiency and to reduce system administration effort.  The reduction in
time to boot would mostly be useful for demos and benchmarks.

Donald Becker				becker at
Scyld Computing Corporation
410 Severn Ave. Suite 210		Second Generation Beowulf Clusters
Annapolis MD 21403			410-990-9993

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