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Incorrect Tape used capacity

Created: 14 Nov 2013 | 3 comments


I have 2 backup sets. backing up the same files.  After the backup.  two tapes displayed different Statistics.  I also dont know if the other tape was resue but both tapes have the same contents.

Is Statistics diplaying the correct available and used capacity or it also displays all the bytes written on the tape?



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pkh's picture

What makes you say that both tapes have the same contents?  The job that writes to the second tape could have appended to the tape and thus it has more data on it.

Vishal Shinde's picture

Hello Jayson,

Backup Exec gets this information from firmware of the device (It is not generated by the application itself.) and these statistics may change, even after same data going to both tapes.

As there is hardware involved to perform the digital recording on the magnetic strip and sequential linear methodology is used to arrange/write data in long parallel tracks that span the length of the tape.

It is difficult to get to identical tapes with the exact same value for the recording density. (Micrometer/character).

Having said that, the statistics shown up suggests that the tape is being reused.



Vishal Shinde

Sr.Learning Consultant

Symantec Education Services

Larry Fine's picture

The "hours in use" is a BE value from the BE database.  Simply based upon the "hours in use" and the "data" differences, I would say these two tapes were used differently.  Probably the second tape was appended to, as PKH suggested.

I noticed that your "data" differed from the first number in "used capacity", but yet your compression was "1:1".  this doesn't make sense as those numbers should be very close to each other if there is no compression.  Since your "used cpacity" is higher than your "data", I suspect a clogged tape head or a very low write speed (basically you are using more tape than you should have, ie negative compression).

I also noticed a very low "bytes read" value, which suggests that you are not running verify after your backups, which is risky.

What tape drive and what version of BE?

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