This is something it took me two years of using BackupPC before I realized... 
BackupPC doesn't treat "full" and "incremental" quite the way you expect.

When BackupPC does an rsync incremental, it compares to the last full for 
purposes of deciding what to download and *then* does deduplication against the 
pool.

If you do a full on Sunday, and then a user saves a 100G file to the client, 
every rsync incremental will transfer the entirety of that 100G of data, over 
and over, until that file is backed up in the next full.  So if you take one 
full and never take a full again, your incremental sizes will keep growing, and 
BackupPC will keep downloading the same data over and over.

If you do what you want, you'll actually be creating the problem you're trying 
to avoid.

rsync full backups don't download all the raw data every time... the main 
reason they take longer is running checksums against every file instead of just 
the files that have changed meta-data.  If a full transferred all the data 
every time, full backups of my remote server would take hours instead of 30 
minutes.  It's still taking advantage of rsync to not transfer bytes it doesn't 
need.

--
Carl D Cravens ([email protected])
"Then I will smite thee with adware!" - Bucky Katt


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