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Low LTO5 Tape Usage

Created: 03 Jul 2013 • Updated: 23 Aug 2013 | 3 comments
This issue has been solved. See solution.

In last nights ejection, I had:

828gb on one tape
587gb on one tape
I have seen some tape ejections put as much as 2.7tb on a tape for monthly vaults, or 1.1tb on a daily.

Backup virtual servers (on ESX 4.1), Windows and Exchange to a Data Domain VTL
Backups occur 4-10am for Virtual servers.
Other backups occur 10pm-12am, 2am-5am, 6am-10am.
The Vault starts at 3:30am and continues through 10am.
I have 4 volume pools for the tapes:  2 for differentials, 2 for full-backups.
(There are 2 offsite locations tapes are sent to).
The properties of these pools have the following setting, "Maximum number of partially full media: 1"

NetBackup v7.5.0.5 running on Windows 2008-R2
LTO 5 tapes; 1.5tb native, 3.0tb compressed
 

What process is NetBackup using to get a new tape; when it should be putting upto 2.9tb on each tape?

Operating Systems:

Comments 3 CommentsJump to latest comment

mph999's picture
The process is very simple, and in fact is nothing to do with NBU.
 
NBU has no understanding of tape capacity, in fact, if left alone it would use the same tape 'for ever'.
 
NetBackup passes data to the operating system, one block at a time, to be written to the tape drive. NetBackup has no understanding of tape capacity. In theory, it would keep writing to the same tape "forever".
 

When the tape physically passes the logical end-of-tape, this is detected by the tape drive firmware. The tape drive firmware then sets a 'flag' in the tape driver (this would be the st driver in the case of Solaris). There is still enough physical space on the tape for the current block to be written, so this completes successfully. NetBackup then attempts to send the next block of data (via the operating system) but now the tape driver refuses, as the 'tape full' flag is set. The st driver then passes this 'tape full' message to the operating system, which passes it to NetBackup.  Only when this has happened will Netbackup request the tape to be changed.

Or put more simply, the tape becoming full cannot be controlled in anyway by NBU.  Additionally, the amount of data written to the tape is dependant on how 'compressible' the data is, and again, cannot be controlled by NBU.

Low amounts of data written to a tape can have various causes ...

1.  Be totally normal  (data is not very compressible)

2.  Drive hardware fault

3.  Tape driver fault

4.  Tape firmware fault

Martin

 

Regards,  Martin
 
Setting Logs in NetBackup:
http://www.symantec.com/docs/TECH75805
 
Marianne's picture

Are these tapes marked as FULL? 
Or was that the only amount of data that was backed up?
2 tapes because you have 2 Volume Pools for Differentials?

Please post output of 'nbemmcmd -listmedia -mediaid <media-id>' for these 2 tapes.

Supporting Storage Foundation and VCS on Unix and Windows as well as NetBackup on Unix and Windows
Handy NBU Links

mph999's picture

Ahh, good point Marianne, the tapes may not be full ...

In that case :

http://www.symantec.com/docs/HOWTO32854

 

M

 

Regards,  Martin
 
Setting Logs in NetBackup:
http://www.symantec.com/docs/TECH75805
 
SOLUTION