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Those utilities are indeed just that: utilities. They work damned well, but they're not intended as a backup solution. In true unix philosophy, they are a piece of the puzzle ...
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- 02-09-2006 #11
Those utilities are indeed just that: utilities. They work damned well, but they're not intended as a backup solution. In true unix philosophy, they are a piece of the puzzle - they can do the raw movement of data in an addressable format to a file or streaming device. Lower than that is dd. What rajeshk is referring to is a level much higher - something that manages the entire mess - from incrementals to full backups, archives, realtime backup buffers, yadda yadda. More often than not, the commercial companies create their own format to tape other than tar or bru, simply because they need to embed so much more metadata. The one we use is really fire and forget - once a week you need to make sure there's enough tapes in the Superloader, then leave it. Auto-cataloging systems, tape age, on and on. It's a wonderful thing precisely because you *don't* have to deal with all that. Recovering is a dream. More often than not I'll notice some little file got blown away, I click through a tree display, find it from the last backups, click-click, go back to work, and 5 minutes later the file has returned.
If you were doing that with a manual tar method, you'd be hunting through "tar -tv" listings with grep, finding the tape, load it, write a manual tar command...ech.
- 02-14-2006 #12
- Join Date
- Jan 2006
Well now i will try to put my doubts much simple and straight forward.
* Backup / Restore is done on tapes.
What is the format of the data (backup data) or which file system is used to write on to the tape while taking up the backup?
Is it taken care by the backup/restore utility or the tape drivers.?
I understand that backup/ restore utility is a third party software which is independent of the tape drives (hardware) used in system. But linux must have to support the tape devices, means necessery drivers must be avialable.
Any kind of suggestions/ advice is welcome.
- 02-14-2006 #13
It's handled by the application. For instance, tar writes in tar format, bru writes in bru, etc. However, in the end it's just data blocks on a tape. A really low level way to access this is with dd - you literally define the size of the blocks and away you go - in or out. In fact, you can use dd to extract data from a tape and pipe in right in the command line to a utility like tar for extraction(sometimes this is necessary when massaging certain older styles of tapes from older backup systems). However, to do any serious management you'll want to have metadata in there, that's what bru and more highlevel applications do. The driver just ensures the data moves back and forth properly. Much of the time the tape drive is SCSI, and this is handled by the drivers in the kernel. More sophisticated devices like an SDLTII Superloader might have their own driver for efficiency, however.
I'm not sure *exactly* what it is you want to do. If what I'm saying isn't helping, you might want to explain that and it will make the responses more clear. It's a big topic with a lot of history(since backups have been around since the begininng ).