Forum Discussion

Joseph_TKLee's avatar
Joseph_TKLee
Level 4
13 years ago
Solved

How much free space in a tape

Hi guys,

Is there any way to check how much free space left in a tape?

I am using NB 7.5

Thanks,

Joseph

7.5
Backup and Recovery
NetBackup
  • RamNagalla's avatar
    RamNagalla
    13 years ago

    hi

    you can see the how much of data written using the below command, or from the GUI-> medias(under Kilobytes tab)

    bpmedialist  -m <mediaid> -U

    so based on the media size that you use, you can caulcate the amount of free space left for future jobs..

    lets say if you are using the LTO-5 tapes.. with capacity of 1.5 TB.

    and bpmedialist is showing KBwritten as 700GB... so free space is 1.5 - 700 = 800GB.

    Generally EMM server will take care all this behalf of us... :-)

    hope this helps.

7 Replies

Sort By
  • RamNagalla's avatar
    RamNagalla
    Moderator
    13 years ago

    hi

    you can see the how much of data written using the below command, or from the GUI-> medias(under Kilobytes tab)

    bpmedialist  -m <mediaid> -U

    so based on the media size that you use, you can caulcate the amount of free space left for future jobs..

    lets say if you are using the LTO-5 tapes.. with capacity of 1.5 TB.

    and bpmedialist is showing KBwritten as 700GB... so free space is 1.5 - 700 = 800GB.

    Generally EMM server will take care all this behalf of us... :-)

    hope this helps.

  • Yasuhisa_Ishika's avatar
    Yasuhisa_Ishika
    Level 6
    13 years ago

    Maximum tape capacity depends on tendency of data you when hardware compression is enabled because compression ratio of data affect amount of space required on tape. Some sort of data - especially already compressed ones like jpeg, mpeg or so - has low compression ratio, on the other hand, some sort of data like text file has high compression ratio.

    So it is hard to estimate free space on tape exacty. But you can guess it by amount of data the tape which contains similar data become full with.  

  • Joseph_TKLee's avatar
    Joseph_TKLee
    Level 4
    13 years ago

    Thanks guys,

    All your advice which I already aware of.

    We are also using Networker which shows the function of the usage percentage of a tape.

    I know it is not precise but looks goood. :)

     

  • Marianne's avatar
    Marianne
    Level 6
    13 years ago

    There is NO WAY any backup application can know that.

    An application that is displaying this, is merely guessing based on averages. How does any backup application know if you hcart tape is LTO1 or LTO4? And what kind of data you are backing up?

  • Andy_Welburn's avatar
    Andy_Welburn
    Level 6
    13 years ago

    Just to show how difficult this could be to determine:

    Using Nagallas example of bpmedialist -

    # bpmedialist -m 300714 -U
Server Host = server1

 id     rl  images   allocated        last updated      density  kbytes restores
           vimages   expiration       last read         <------- STATUS ------->
--------------------------------------------------------------------------------
300714   8    182   07/28/2012 06:00  07/28/2012 06:00  hcart3  1277324207     0
              MPX   07/28/2013 06:00        N/A

     

    So this media *still* has writeable capacity (there is no FULL status) & it has written 1277324207Kb (over 1Tb). Now the density is HCART3 - this could be *anything* as essentially it is just a label - however, I can confirm that this is an LTO3 which are advertised as 400/800 i.e. 400Gb native/800Gb compressed capacity.

    So, how do I work out how much more I can write to this tape? The *closest* would probably be what Yasuhisa has stated:

    guess it by amount of data the tape which contains similar data become full with.

  • Kiran_Bandi's avatar
    Kiran_Bandi
    Level 6
    13 years ago

    I am not sure if i can write all this here, but proceeding...

    It does show but it actually calculates against the native capacity of the tape. That is why you can see huge amount of data being written to tape between 100% - FULL. The thing here is you can define the capacity of the tape that is being used laugh. If you say my LTO4 tape is of capacity 10TB, Networker starts dispalying 10% used after writng 1 TB of data to tape laugh.

  • mph999's avatar
    mph999
    Level 6
    13 years ago

    The overiding factor in all of this is that any 'calculation' will only be an estimate.

    NBU has no understanding of tape capacity, and would in fact 'write' data quite happily to the same tape for ever.

    What actually happens is that when the tape becomes full, this is detected by the firmware of the tape drive, and a 'flag' is set in the tape driver.  The tape driver then informs NBU that the tape needs to be changed as it is full.

    Martin