you can probably write a custom script that will do what is needed, and have the Hobbit client run it wherever you need it. Then you can write another script on the server side to "catch" the data and set up the RRD calls. There are several moving parts, but Henrik has done a nice job explaining what needs to be done, and provides a helpful example.
I use this function for a number of custom measurements, and it ticks like a watch. Took me a few hours to get the first one working, and the rest were pretty easy after that.
GLH
From: Jerry Yu [mailto:jjj863 at gmail.com]
Sent: Thursday, August 03, 2006 8:04 AM
To: hobbit at hswn.dk
Subject: [hobbit] monitor a series of files for absolute size(alert & trending)
greetings,
I need to monitor some os and db backup files for their sizesfor alert based on absolute sizes as well as rrd trending. Does Hobbit do this now? I am running 4.2-RC-20060712 on CentOS 4.3/i386.
A twist is the file names are timestamped(os-backup-YYYYMMDD-HHmm.star.gz). any suggestions/tricks? I thought of making a copy to a fixed name for monitoring, but it is kinda expensive due to the size of the backups themselves.