On Mon, 2006-05-29 at 11:07, Bill Hudacek wrote: > However, I was very dismayed to find the word "incremental" being used > to describe the backups performed between full backups. it's pervasive > throughout the docs, FAQs, and this news group. > > As a (former, in a past life) UNIX systems manager for an international > corporation's data center in the U.S., I dealt with these kinds of backups: > > 1. Full > 2. Differential > 3. Incremental > > A differential the day after a full would backup only those files that > changed that day. A differential the day after that would back up all > files that had changed since the full backup - in other words, the > contents of the first day's differential backup was included in the > second day's backups. This was not as bad as it sounds, as a file > deleted before the backups on day 2 would still appear on day 1's > differential backup. > > Incrementals, however, meant only files changed since the last backup > "of any kind" (full, differential, incremental) would be backed up.
I've heard the differential term before, but can't place it with any of the standard unix tools (tar, dump, cpio, etc.). Can you point out a man page that covers this distinction? > I would have been happiest with a three-tiered backup model in backuppc, > as my use of an "on-line backup server" means having 1 full, the latest > differential (say, from "full + 3 weeks"), and three incrementals to > restore is not an inconvenience at all. These distinctions don't make a lot of sense with the way backuppc does things. All duplicate copies are merged, so it doesn't take much more space to store another full compared to an incremental. Backuppc always merges the full and incremental during the restore so there is no apparent difference there either. The differences really relate to the transfers and the quirks vary according to the transfer method. > However, having said that - with my BackupPC environment, instead of > running a full backup once a month, and having differentials weekly, > with incrementals daily, I simply run fulls weekly and thus the > "differentials" that backuppc calls "incrementals" do not ever approach > the cost of a full backup (which I would consider not just an > inconvenience but a serious problem). With tar and smb fulls actually transfer a complete copy over the network but duplicates are identified and replaced with links on the server side. Incrementals work strictly by timestamp and thus will miss old files under renamed directories in the tar case (working with ctime) and any backdated file (copied with any method that preserves an old timestamp) in the smb case. With rsync, all files are checked but the difference is that the incremental runs check only directory entries (timestamp/length) on existing files - fulls do a block checksum comparison with the rysnc algorithm. The comparison is always against the last full run, though, so incrementals keep growing in size. It might be possible to tweak the options in the rsync command to make a full run also trust the directory information to make fulls go faster. -- Les Mikesell [EMAIL PROTECTED] _______________________________________________ BackupPC-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/backuppc-users http://backuppc.sourceforge.net/
