Forum Discussion

rafanto's avatar
rafanto
Level 5
6 years ago

Netbackup and Tapes

Hi,

Please your help, we have a NBU 8.0 and appliances 5240 with a library / tape drive LTO7.  The cartridges, as you know, have 6TB (native) and 15TB asumming a 2.5:1 compression.

With this context, we are duplicating through SLP images from appliances to this tapes, but we had encountered various "strange" scenarios, for example:

This tape is FULL, and the space consumed is 21368712128 KB, aprox 19.9TB, is correct tha value? A tape could store more than 15TB its theorical capacity?

 

 

 

And this escenario, we have tapes with 26TB, and other tapes that have 3.5TB or 2.9TB and NBU, for some reason, can't write anymore, and the space is waste.

How NBU handles the writing on tapes ? The information is the same (SQL Data Bases) on all tapes.

Please, we need an explication from people with experience with this type of issues

Regards

Rafael

  • NBU has no understanding of tape capacity, it would write to the same tape forever if it could.

    A tape is only marked full, once it passes the 'tape is almost full' mark that is written to the tape during manufacturing, this is detected by the tape drive firmware.  This sets a 'tape is almost full' flag in the OS tape driver.  There is still a bit of space left at this point, so the current block of data being written will complete.  NBU then sends the next block of data, but it is refused by the tape driver, who then tells NBU the tape is full.

    At this point, NBU knows to change the tape.

    A tape can hold more than it's capacity - for example database sparse files can 'look' very big, but contain 'not much' and so take up no space, hence you can appear to get a lot more on the tape.

    Sometimes it goes the other way, and you get under the native (non-compressed) capacity - this signifies a fault, usually the tape driver, or sometimes the tape drive firmware or hardware - I have never in 11 years seen this to be the fault of NBU, simply because NBU is not able to mark a tape full on it's own.

     

     

  • rafanto 

    In addition to excellent advice from mph999, I'd like to respond to this:

    .... other tapes that have 3.5TB or 2.9TB and NBU, for some reason, can't write anymore, and the space is waste.

    I noticed that the tapes in your screenshot have retention levels of 8 and 9. 
    NBU will only append more retention level 8 backups to current ret level 8 tapes. 
    Same for ret level 9. 
    NBU does not mix retention levels on the same tape. This can be changed, but is NOT recommended. 
    When a tape is full, it can only be overwritten once ALL images have expired.
    So, while ret level 8 images will expire, level 9 will never expire and tape cannot be re-used.

    NBU will append to existing tape if all of the following is true:
    Tape is in the robot
    Same media server (if more than one media server, media can be shared, but not enabled by default)
    Same Volume Pool as previous images
    Same Retention Level as previous images
    There is no hardware expiration date on the tape (manually done in Media section of the GUI).

    I will provide URLs a bit later (if time permits). 

  • rafanto 

    In addition to excellent advice from mph999, I'd like to respond to this:

    .... other tapes that have 3.5TB or 2.9TB and NBU, for some reason, can't write anymore, and the space is waste.

    I noticed that the tapes in your screenshot have retention levels of 8 and 9. 
    NBU will only append more retention level 8 backups to current ret level 8 tapes. 
    Same for ret level 9. 
    NBU does not mix retention levels on the same tape. This can be changed, but is NOT recommended. 
    When a tape is full, it can only be overwritten once ALL images have expired.
    So, while ret level 8 images will expire, level 9 will never expire and tape cannot be re-used.

    NBU will append to existing tape if all of the following is true:
    Tape is in the robot
    Same media server (if more than one media server, media can be shared, but not enabled by default)
    Same Volume Pool as previous images
    Same Retention Level as previous images
    There is no hardware expiration date on the tape (manually done in Media section of the GUI).

    I will provide URLs a bit later (if time permits). 

  • NBU has no understanding of tape capacity, it would write to the same tape forever if it could.

    A tape is only marked full, once it passes the 'tape is almost full' mark that is written to the tape during manufacturing, this is detected by the tape drive firmware.  This sets a 'tape is almost full' flag in the OS tape driver.  There is still a bit of space left at this point, so the current block of data being written will complete.  NBU then sends the next block of data, but it is refused by the tape driver, who then tells NBU the tape is full.

    At this point, NBU knows to change the tape.

    A tape can hold more than it's capacity - for example database sparse files can 'look' very big, but contain 'not much' and so take up no space, hence you can appear to get a lot more on the tape.

    Sometimes it goes the other way, and you get under the native (non-compressed) capacity - this signifies a fault, usually the tape driver, or sometimes the tape drive firmware or hardware - I have never in 11 years seen this to be the fault of NBU, simply because NBU is not able to mark a tape full on it's own.