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Duplication and backup size on tapes

Level 2

Hello everyone,

I have a question about duplication and backup size on tapes:
I use LTO6 tapes, When I perform an Incremental backup the tape reaches a full size of 6TB but When I make a FULL backup the tape reaches a full size of 3.5TB.
Is there any reason for this? Is there a setting that is responsible for this configuration?
Netbackup version 8.1 build 0049




What kind of data are you backing to these tapes??

If the data is already compressed or less compressible you may not get desired results. I am thinking FULL backup has more data that cannot be compressed enough on Tape than incremental backup that you are doing.

Partner    VIP    Accredited Certified

1) NBU isn't comressing data while writing it to a tape drive because drive does it by itself on HW level, so you can't affect it using NBU. 

2) Theoretically, you might have such bizarre workload that data changes all the time but I hardly believe in that. In worst case you'll get Inc backup as big as Full backup. The only explanation I have is that somebody mounts extra filesystem during the workweek and unmount it before weekend.

Level 6

Well excude and include lists can be configured by schedule so its possible some stuff is being excluded from fulls but not incrementals etc; also pre and post notify scripts can be configured by schedule so its also possible some logic is being run before fulls but not incrementals or vice versa.

You can also try and compare what is actually in a full vs an incremental backup via the BAR GUI or "nbfindfile", "bplist" or bpflist" commands (though their syntax can be challenging)...


Partner    VIP   

As long as you get a tapes native capacity you are good to go.

Level of compression depends on data being written to tape. 

quick check: If most tapes marked as FULL has lager than native capacity written to them, don't worry if some tapes only only have 3.5 TB.


The backup I make is of VMWARE virtual machines with daily backup defined as incremental and also with the weekly backup defined as Full backup.

In the daily backup the tape receives 6TB and becomes in status "full" and in the Weekly backup the tape receives only 3.5TB and becomes in status "full".

Is it supposed to behave like this even though in both cases I backup the same virtual machines?

Partner    VIP   

Don't think anyone of us can tell you that for sure.

To analyze the state, you need to identify the files being changed inside the VM's and assess the possible compression value. Then take a look at the rest of the files to assess possible compression rate. 

Regarding full backups:  LTO6 has a native capacity of 2.5 TB, and since you get 3.5 TB on full, and binary files compress at a ration of about 1.5X to 2X, you are pretty much spot one.