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How NetBackup decides how much data write on tapes

Please help to understand how NetBackup decides how much data write on tapes.
I have created a new backup policy. It creates two copies with differents retention levels, let say 15 and 16.
All data goes to tapes directly.
After backup job has been completed I've got the following:
- One tape with RL15 has 3.6TB of data and still has active status.
- Two tapes with RL16 has 3.0TB and 0.6TB of data. One tape (3.0TB) has status full, the second one is still active. The sum of data (in KB) on tapes with RL16 is the exactly same as on tape with RL15. All tapes was taken from a scratch pool. There were no any data on them before.
Why NetBackup split data on tapes such way? Why not equally on each tape(s)?
Thank you.

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Re: How NetBackup decides how much data write on tapes

tapes can have bad spots found at the factory and so formatted in - tapes can later develop bad spots which the tape drive has to then handle and mark/record on the mini-RFID chip inside each tape cartridge - tapes can actually be of different lengths internally (from the factory) - the streaming rate can affect tape writing, i.e. the tape drive may insert many "IRG" (inter record gap) if the data receive rate at the tape head cannot keep up with the tape winding speed.

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Re: How NetBackup decides how much data write on tapes

This is not a NetBackup issue. The tape drive firmware sends a message to the OS and NBU that the tape is full.

Please see these excellent answers from @mph999 :
https://vox.veritas.com/t5/NetBackup/The-backup-size-on-the-tapes/m-p/710551#M190323
and https://vox.veritas.com/t5/NetBackup/Data-storing-issue-on-Tapes/m-p/662369#M173226

Official TN: https://www.veritas.com/support/en_US/article.100014480
See 'Tapes not reaching capacity'.

 

Accepted Solution!

Re: How NetBackup decides how much data write on tapes

tapes can have bad spots found at the factory and so formatted in - tapes can later develop bad spots which the tape drive has to then handle and mark/record on the mini-RFID chip inside each tape cartridge - tapes can actually be of different lengths internally (from the factory) - the streaming rate can affect tape writing, i.e. the tape drive may insert many "IRG" (inter record gap) if the data receive rate at the tape head cannot keep up with the tape winding speed.

View solution in original post