System update spec proposal

[tridge at samba.org]

Scott,

 > Rsync documents using 100 bytes per file, so that's 100M of core
 > required.

That "100 bytes per file" is very approximate. It also increases quite
a lot if you use --delete and also increases if you use
--hard-links. Other options have smaller, but non-zero, impacts on the
memory usage, and of course it depends on the filenames themselves.

If rsync is going to be used on low memory machines, then it could be
broken up into several pieces. So do multiple rsync runs, each
synchronising a portion of the filesystem (eg. each directory under
/usr).

Alternatively, talk to Wayne Davison about rsync 3.0. One of the core
things that brings is lower memory usage (essentially automating the
breakup into directory trees that I mentioned above).

I had hoped to have time to write a new synchronisation tool for OLPC
that would be much more memory efficient and take advantage of
multicast, taking advantage of a changeset like approach to complete
OS update, but various things have gotten in the way of me
contributing serious time to the OLPC project, for which I
apologise. I could review any rsync based scripts you have though, and
offer suggestions on getting the most out of rsync.

Cheers, Tridge