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Please Help - tape capacity

Created: 02 Apr 2013 • Updated: 16 Apr 2013 | 5 comments
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Please help:
in my symentec netbackup media sometime showing full so early.for example: 2114541984 showing full and sometimes 3110560576 showing full.why like this my admin ask me why such a change in your tape media. full so early means i have to buy another media which is very expensive for me. although we know tape media storgae capacity is 1.6 T.

Sorry for my bad english

my netbackup version is 7.1

please help its urgent

Operating Systems:

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sazz.'s picture

It seems you are using LTO5 Tapes which have a capacity of 1.5TB/3.0TB (compressedd) if you get 2:1 compression. As per your output you are getting a good compression on the tape. The compression is totally dependent on the data that is getting backed up. Sometimes you get files which can be compressed much but at the same time the database files can't be compressed much.

The netbackup just sends the data to the tape library and it is hardware that does the compression to its capacity. The Policy compression is not recommended and should be left to hardware to take care of compression. Tell your admin that compression can't be exactly same all the time and varies according to data.

RamNagalla's picture


the amount data that is writing on the tape is dapends on the compression ratio and this compression ratio always depends on the type of data

generally this compression handles by the tape drive, which is netbackup not aware..

I belive that number that you have provded in KB 2114541984( around 2 TB) and 3110560576(around 3 TB)

though you know that the tape capacity is 1.6 TB, due to the compresssion it able to take more than that..

see below how compression works in different types of data

Note the following levels of compressibility, in descending order:

  • Plain text

    Usually the most compressible type of data.

  • Executable code

    May compress somewhat, but not as much as plain text.

  • Already compressed data

    Often, no further compression is possible.

  • Encrypted data

    May expand in size if compression is applied.

mph999's picture

Netbackup has no understanding of tape capacity, it does not know when a tape becomes full.

The firmware of the drive detects the tape full, and tells the tape driver, which then tells Netbackup.

Therefore, there is nothing that you can do in Netbackup to control of adjust this.

As mentioned, media will hold different amounts of data when full, due to some data compressing more than others.  Other issues that can affect amount of data the tape can hold are 'bad' firmware and hardware faults on the drive,.


Regards,  Martin
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Moinul's picture

Thanks guys for your great opinion.


Marianne's picture

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