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How do Netbackup intract with OS for wrtiting data on Tapes

Created: 05 Jul 2012 • Updated: 10 Jul 2012 | 2 comments
rajeshthink's picture
This issue has been solved. See solution.

Well This is not a Doubt but a query for Drives and Netbackup , we know netbackup has very littile introvention when writing to tapes.

But what excatly happence with NBU and OS and how do they intract with each other to write data on Media.

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mph999's picture

bptm send various scsi commands, for example to  set the scsi reservation on the drive, and then to check when the tape is loaded, and ready to be used, for example 'test unit ready' / 'mode sense'.

Depending on OS, these commands may go via the pass thru driver (eg. sg on solaris).

Once the drive is ready, the data is passed from the NBU data buffer to the os which writes it to tape via the tape driver.  Also, when NBU sends the data to te OS, it sends the blocksize that should be used (SIZE_DATTA_BUFFERS).  The positioning of the srive is done via the OS, this is where you see things like MTSFS / MTBSF in the bptm log - obviously, NBU reequests the positioning, but the actual commands are sent via the OS tape driver.

After a fragment is written, and/ or end of backup, NBU carries out a position check, asking the drive what position it is at, and comparing this to where NBU has calculated the tape should be.  For example, this is how NBU would detect a SCSI rewind, it can't detect it when it happens (as it's not writing to the drive) and neither can the OS.

At the end (I think) , NBU checks for any TAPEALERTS that the drive has logged, and these would be dispayed in the logs/ error report.

SImple as that.

Martin

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

Just to check did any library hardware info also write into casettle, or just purely client data only?

Many thanks.