Tape Device Names / Functions

[Roomer]

I am currently coding a new backup script and am a little stumped on the available tape device names and their secific functions.

I have a AIX book which very briefly explains them, but it's pretty vague.

Here is an example of the entry...

Device Name Rewind on CLOSE Retention on OPEN
/dev/rmtX Y N
/dev/rmtX.1 N N

Can anyone explain to me what the 'Retention on OPEN' actually means..

If I specify multiple volume groups within a script (savevg) will the backups overwrite each other.

 

[KenCunningham]

Roomer, are you sure it's not 'retension on open'. All this means is that before starting a save, the drive retensions the tape, thus avoiding possible problems with slack tape against the heads. I would have thought that as long as you're using the 'no-rewind' device (ie the devisce with an N in the rewind on close entry, you should be OK to do multiple saves on the same tape.

Hope this helps.

 

[aixqueen]

Tape Format Specification
_______________________________________________
| | Rewind | Retension | |
| Tape Drive | when | before | Density |
| Device Name | finished | starting | Used |
|_____________|___________|___________|_________|
| /dev/rmtx | Yes | No | #1 |
| /dev/rmtx.0 | | | #1 |
| /dev/rmtx.1 | No | No | #1 |
| /dev/rmtx.2 | Yes | Yes | #1 |
| /dev/rmtx.3 | No | Yes | #1 |
| /dev/rmtx.4 | Yes | No | #2 |
| /dev/rmtx.5 | No | No | #2 |
| /dev/rmtx.6 | Yes | Yes | #2 |
| /dev/rmtx.7 | No | Yes | #2 |
|_____________|___________|___________|_________|
x=tape# (ex: rmt0)

If you are stacking your backups you do not want to use retension on open for any other backup but the first...what it does is go to the end of the tape and back to the beginning... if you are stacking....in a script....you want to start where you left off
..........

Retension

Setting the Retension attribute (for chdev, the ret attribute) to yes instructs the tape
drive to retension a tape automatically whenever a tape is inserted or the drive is
reset. Retensioning a tape means to wind to the end of the
tape and then rewind to the beginning of the tape to even the tension throughout
the tape. Retensioning the tape can reduce errors, but this action can take several
minutes. If you specify the no value, the tape drive does not automatically retension
the tape. The default value is yes.


Hope this helps?