Netbackup showwritten above 1.0TB on single LTO-2 tape(200/400)

[Rohit_Phiske]

Hi,

I have come across a complicated issue.The actvity monitor of my server installed with veritas netbackup enterprise master server 5.0 shows that it has written above 1.0TB data on one single LTO-2 tape (200 / 400GB capacity).This is highly impossible and also the tapes written in similiar manner are getting faulty.This is happening for many jobs.

Pls suggest what may be the reason for the same and the resolution at the earliest for the same.

Regards
Rohit

[Anthony_Langdon]

It is not highly impossible, if the data being backed up is highly compressible. The LTO-2 drive will normally struggle to write more than 400GB of data to single cartridge if the data is 'ordinary' files, but if the data is highly compressible you might well get 1TB on a single tape. I'm currently testing this theory. I might have an answer for you on Modday.

The faults may be unconnected.

Do you knwo that the data being written is not highly compressible?

Tony

[Stumpr2]

Tony is correct. Some files, especially db's, can get great compression!
Perhaps you have stumbled onto some issues with an image spanning tapes?

[DavidParker]

5:1 compression isn't all that rare, no?

My Vault created a tape with 890,780,727 KBYTES on it yesterday.
Pretty good performance, wouldn't you say?

[Rakesh_Khandelw]

You can see these kind of high numbers on single tapes if your data on particular tape contains lot of big DB files. The way DBAs define data files in database, they assign file name and size of the file to be used. If file size is say 2 GB, you will see 2GB used at Filesystem level but within database you may be using only 10% of 2GB. When NetBackup backup these kind of files it get high compression rate because it's compressing the empty space within the file.


BTW, I have lots of LTO-3 tapes with more than 2 TB on one tape. :)

[Rohit_Phiske]

Hi,

The database backedup is Oracle.

Are u able to restore the tapes backed up successfully?

Regards
Rohit

[Rakesh_Khandelw]

Restore works like any other standard restore. At least I and my support staff haven't seen any issue with these backups neither in test environment nor in production environment ( we do restore prodcution environments for SOX, DR and other purposes). long story short, never had any issue with restores from these so called overloaded tapes.