[rdiff-backup-users] Magic increments via LVM snapshots idea

[Steven Willoughby]

Hello everyone,

   I think it is possible to combine rdiff-backup and LVM snapshots to 
have incremental backups on the same machine without having two full 
copies of the data set.  What follows are some instructions on how I 
think this would be done:

   First, set up LVM such that you have one large partition for your 
data, one small partition for your incremental backups, and enough free 
space to make snapshots.  For sake of simplicity, pretend you mount them 
as follows:

/data
/increments
/snapshots/xx

1. Create a symlink for rdiff-backup-data (ln -s /increments 
/rdiff-backup-data)
2. Create snapshots/1 (a snapshot of /data)
3. Wait a few hours (or day, or whatever) for data to change
4. Create snapshots/2 (another snapshot of /data, now there are two 
active snapshots)
5. Run rdiff-backup /snapshots/2 /snapshots/1
6. Destroy snapshots/1
7. Repeat steps 3-6 indefinitely, incrementing the snapshot number each time

   I not yet had a chance to try this out on a computer but it seems to 
work in my head.  I am posting it in the hopes someone might find it useful.

Steven

Note: If you ever accidentally destroy both snapshots then you will lose 
history for any file that has changed since the last time rdiff-backup 
has run.  (This can be checked with --verify.)

Another note: Step 5 will update the oldest snapshot so that it is 
identical to the newest.  Since the oldest is immediately destroyed 
after rdiff-backup runs, this update is not necessary and rdiff-backup 
could be patched to skip it and only create increment files.

Yet another note: You will need to pass the -b and --exclude 
/snapshots/2/rdiff-backup-data options in step 5.