[NCLUG] Backup idea

[grant at amadensor.com]

I have been thinking about a new backup idea, but first, here is my  
current setup:

I have a separate mirrored array for backups.   It uses a daily cp to  
copy the files to a dated copy using hard links, then uses rsync to  
overlay only the changes.   It also daily deletes the oldest backup.

This is good, except for one little thing, it is hard to manage when  
the disk gets close to full.  Sometimes I need to manually delete the  
oldest backup an extra time to leave enough slack for the next day's  
rsync delta.

Here is my idea:
Rebuild the backup partition using LVM.   Do a daily rsync to it, then  
do a snapshot.

Will this succeed in removing the oldest one any time I run out of  
space?   I know that it will invalidate the snapshot, but will it drop  
it and free up the space?  What happens if that snapshot is mounted  
when it gets full, does it get unmounted and removed, or does the  
whole volume group go into a state of stuck?

I wish I had extra hardware to play with this on, but right now I  
really don't, so I am hoping someone else has done this.