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How data is stored on a backup tape.

Posted on 2004-09-26
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Could someone help me to understand how Data is stored on a backuptape, How is it indexed. When doing a differential backup, is the tape formatted every  time it`s being read to? Should the tape be formatted now and then to avoid problems?  Why? And please give me all informations that You think is relevant to this topic.
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Question by:TorgN
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by:cooledit
ID: 12158058
hi, there

Backup's is stored as single files on the tapes. The indexing is done by individual program's but in theory if you do a backup from Windows Native backup or let's say Veritas then each differental program's is capable of restoring the data.

For the differental backup the tape is not erased. If you wanna reuse tape's then it's better to format it, relabel it.
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cyrax earned 250 total points
ID: 12158128
TorgN,

Data is stored on a backup tape sequentially. This means that data is written to the tape in one contiunous, long stream. It can be likened to the music on an audio tape that plays a song as the tape advances.

Indexing is used to provide a reference to all of the portions of data on the tape. If for example, a tape has a stream of data with each data portioned into five sections, labelled 1, 2, 3, 4, 5. If you wanted to access some particular data at portion '4' of the tape, the index will tell the operating system or backup/restore program where on the tape the data is located relative to the other data.

A differential backup on the other hand, looks at the current data being backed up and compares it with the records of the data on the tape. It will only back up the data that has changed.

Normally the tape will only be formatted if you specify it.

There are many resources on the Internet that explain backup methodologies. Here is one of them:
http://www.pctechguide.com/15tape.htm

Good luck!

-Cyrax-
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by:TorgN
ID: 12158180
Thank you for the help it helped me understand the essense of Tape Backup :)
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