backup query

[khilari]

Well, when u r taking a backup. U use the 0m option. Now, if u r taking a full backup then fine, u nee the 0m option because after the full backup it will just rewind and the header of the tape will come to the beginning to start a rewrite. But I guess when u r taking an incremental backup u need 0mn, because u want to append to what u have.
In cron backups, where u r taking a backup of a particular filesystem every day what would u use. A 0m which would over write the information each time u use that or 0mn which will just keep on appending it till it has no more space left and what happens when it gets full in 0mn. Will it start overwriting at that point or just seize to work….

[A. Clay Stephenson]

Without knowing the type of backup (cpio, tar, fbackup, dd, DP) your question can't be answered. The no-rewind device nodes, start just where the last operation was completed. However, if you are using fbackup, you must always start at the beginning of the media.

In most cases, trying to put more than 1 backup (full or incremental) on the same media is just too easy to mess up so that you have no backup. The exception to this is a commercial package like DataProtector which maintains a database that tells it exactly where to look on a designated media for a desired backup object. That's the only time, I will put more than one production backup on the same media.

[TwoProc]

Here's a format for a very rudimentary system. Your mileage and retention policies will vary.

Make two weeks worth of tapes(minimum) and label them. Walk over to a calendar and for every day, mark the tape label that should be used that day on the calendar. Have an operator change the tape every morning bright and early and match the tape label to the calendar label. Have the other tapes not in used stored in a safe, secure fireproof vault. Don't forget to make archival copies too - not just rotation tapes. Don't forget to effectively and fully destroy tapes after your retention period(old tape data is a security risk too)! Figure out how many times you want to use a tape, then figure out where that lands on the calendar, and then mark the calendar for the replacement of those tapes. Mark on the calendar the days you want to clean tape heads too.

Why not just use one tape?

Because that tape will go bad on you during a backup, and it WILL BE on a day that you have something critical to recover. Or, you'll have a crash or disaster WHILE you were creating the backup, and now you've destroyed the previous backup, and the current backup isn't finished... You'll be standing there with the munged tape in your hand which is your total backup and recovery strategy, wondering what to do next...

Why use two weeks worth of tape (or more preferrably)?

So that you can go back in time and search for files that went missing/bad/corrupt some xxx days ago that went undetected for a while. The more you days you keep in rotation the longer back in time you can go. The more critical the databases/files the further back you should go. Go with what your comfortable with and do a little more than that.