Wouldn't it nice if we could combine the speedy backup and frugal space habits of the incremental backup with the fast restores of the differential variety? Welcome to the third party backup utility: Retrospect from Dantz Development .
Retrospect works in a similar fashion as ntbackup in that it saves its backup data to backup sets. These sets, as in ntbackup, can be stored on tape, magnetic media, or optical media. Retrospect uses three main types of backup: Normal , Recycle , and New Media .
The recycle backup in Retrospect is essentially the same as ntbackup's normal backup in that it backs up everything that it touches. It also erases the contents of the current backup set, zeroing it out so that a new backup may replace it. So if we are backing up our server every day of the week, we might perform a recycle backup on Monday to clear the old backup contents to make room for the new backup.
The normal backup is exactly the same as ntbackup's incremental backup. Retrospect backs up all files that have changed since the last recycle or normal backup, and then marks them as backed up. This gives us the space savings of the incremental backup, as well as the speedy backup times.
New Media Backup
The new media backup essentially preserves all data in a backup set (for permanent archival purposes) and starts a new backup set with a similar name to the previous one.
So how does Retrospect combine the advantages of incremental and differential backups ? Consider this scenario:
On Monday , a recycle backup is run. This backs up everything on the server, and marks all files as backed up.
On Tuesday , a normal backup is run. This backs up all files that have changed since the previous recycle backup on Monday. Once the backup is completed, Retrospect creates a "snapshot" of the server in its backed up condition. This snapshot includes all files that were backed up on Monday and Tuesday.
On Wednesday , another normal backup is run. Again, this backs up all files that have changed only since the last backup, which was Tuesday. A new snapshot point is created that contains all files backed up since Monday.
On Thursday , a normal backup is run. The story is the same: only those files that have changed since Wednesday are backed up, and a new snapshot reference is created.
On Friday , we have a catastrophic loss of data on the server. If we were using ntbackup, we would have had to restore the initial backup, followed by the backups run on Tuesday, Wednesday, and Thursday.
But with Retrospect, all we need to do is restore using the snapshot created on Thursday. The software automatically rebuilds the server as it was when it was backed up on Thursday using all data from the previous backups.