/dev/rmt/0mn or /dev/rmt/0m????

[JMI]

I have done a make_recovery with /dev/rmt/0mn. The copy was aparently right, but when we tried to restore during the boot sequence, it doesn??t work. The problem seems to be a faulty tape, because we had errors about LIF area,...

I suppose that the problem wasn??t due to the device file use in make_recovery sentence, but I??m not sure. Do you know if is better use /dev/rmt/0mn or /dev/rmt/0m?

I know that the first rewind the tape, but I think it would be more normal use the second, and then we have a copy on each tape.
What do you think?

Thank you in advance.

[PIYUSH D. PATEL]

Hi,

you should use it with /dev/rmt/0m

I have doen with that and it has worked fine.

Piyush

[James R. Ferguson · Accepted solution]

Hi:

When making Ignite tapes with 'make_tape_recovery' (or the older 'make_recovery') you should use the "no-rewind" device -- /dev/rmt/0mn.

Regards!

...JRF...

[Helen French]

You SHOULD use a non-rewind device file while doing make_recovery ! It should be /dev/rmt/0mn (no-rewind). For confirmation, check this:

# man make_recovery

btw, it's time to update it with new make_tape_recovery

[MANOJ SRIVASTAVA]

Hi JMI

/0m is with rewind option this rewinds the tape to the start of media after any command is issued ,

/0mn is no rewind option this will leave the tape at the same postion where the old commnad ended .


this is true for read , write commands , for this case I would always use the /0m option and not the /0mn option.


Manoj Srivastava

[David Burgess]

I use

make_recovery -Av

This picks up my tape device and creates the tape fine without specifying the -d option.

HTH,

Dave.

[Mark Vollmers]

Hmmm. seems we have two schools of thought here. why does it matter if it is rewound or not? if you actually have to use the tape, doesn't it have to rewind it to run anyway? any once you finish the ignite backup, you normally don't append anything else to the tape, do you?

Personally, I use 0m, because that was what the last sysadmin used, but I've never had to use it, so I don't know if there is a difference.

Mark

[Patrick Wallek]

Why should you use the no-rewind device? Because, as said above, the rewind device MAY rewind the tape after each command is finished.

Let's look at it this way - You create a make_tape_recovery tape with /dev/rmt/0m. The first thing written to the tape is the boot LIF area so you can boot from the tape. The tar/pax archive is then written to tape AFTER the boot area, BUT is the tape has been rewound and is sitting at the beginning of the tape, you just overwrote the boot area and your make_tape_recovery tape is useless.

If you use /dev/rmt/0mn then you have significantly less of a chance of overwriting the boot area because the tape was rewound after it was written.

I ALWAYS use the no-rewind device. If you look at the man page for make_recovery at the '-d' option you will notice that it says "A no-rewind device is REQUIRED".

That's good enough for me.

[Jack C. Mahaffey]

Good discussion. Should the tape be rewound after the the make_tape_recovery is done so that the tape will be properly position when the tape is used again for another make_tape_recovery?

e.g. mt -f /dev/rmt/0mn rew

jack...

[Patrick Wallek]

Whether or not the tape is rewound AFTER THE ENTIRE make_tape_recovery process is moot. When you eject the tape, it will be rewound automatically by the tape drive. If you do a 'mt -f /dev/rmt/0?? offl' to eject the tape, it will rewind first.

That being said, I have a line in the script I use for creating my make_tape_recovery tapes that does a 'mt -f /dev/rmt/?mn rew' before the make_tape_recovery starts just to be on the safe side. Then I ALWAYS use the no-rewind device in the make_tape_recovery command as well.

[Jack C. Mahaffey]

Thanks... I'm going to follow your example and do the mt -f /dev/rmt/0mn rew before the make_tape_recovery starts..

Thanks for the hints...

jack...