Monday morning

03 Sep 2007 Looking at the schedule, today will be mostly filesystem/storage based, so not of real interest to me.

Pimp My Volumes - Bryn M. Reeves (Red Hat)
Towards a Scalable Device Mapper Snapshot Solution - Jan Blunck (Novell/SUSE LINUX Products GmbH)

Both talks were about the device mapper. Not much to say about it really :) One thing that I found odd is the way snapshots work in DM. A snapshot is an "image in time" of a filesystem. When you take a snapshot of a filesystem, the filesystem state is saved somewhere as it is and you can use it for example backups. While you are doing your backup though, the original filesystem can be changed at will and it will not affect the backup.

A logical approach to this would be that all changed done to the filesystem from the snapshot point onwards, are stored somewhere. The original filesystem plus the changes in that "extra" filesystem, is then the most up to date version of the filesystem. If you ignore the extra filesystem, you just have the snapshot.

How does DM do it ? Instead of keeping the snapshotted filesystem fixed and storing the changes made to it in a separate file, it actually stores the inverse of each change in the file. The snapshot is then actually the currentn filesystem (which is in constant flux) combined with the inverted changes.

Now this doesn't scale well. As the speaker shows, a regular DM filesystem may have a 33MB/s throughput, but when na snapshot is made, that drops to 2.4MB/s

dstat: plugin-based real-time monitoring system - Dag Wieers (dagit)
Already saw most of this yesterday

CPAN6: Collecting collections - Mark Overmeer (MARKOV Solutions)
I thought this talk would be a practical or lowlevel view of how CPAN functions. But instead, it was a very abstract view on a paradigm where people can store any kind of file in an archive.
Through the entire talk I kept thinking: it's time to step off your cloud and do something substantial. But maybe there is a codebase somwehre I'm not aware of ?

In any case, it seems the sponsor of CPAN6 (NLNET) sponsors all kinds of opensource projects involving nentworking. Maybe I can get a fund there for HPPC or something else.