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

[Brian Lee_4]

I have made OS backup with make_recovery
command and " -d /dev/rmt/0m" option.
I have reconfigured root file systems with dds tape backuped with the command above.
Suddenly, I can not boot system with dds tape and error says "Error Reading IPL file".

Theree, I recreated OS backup tape with
"-d /dev/rmt/0mn" and it worked fine.

It confuses me.
Anyone can explain?

[Patrick Wallek]

Sure. You MUST ALWAYS use the no-rewind option for the tape device (/dev/rmt/?mn) when doing a make_tape_recovery.

An extrememly simplified explanation (when using the no-rewind /ev/rmt/?mn):

1) Make_tape_recovery writes the boot information to the tape.
2) Immediately following the boot information is the pax (basically tar) archive of your VG00 filesystems.

So the tape boots then, when finished booting, the tape is at the beginning of the pax archive and the restore can take place.

Now, if you don't use the no-rewind tape (/dev/rmt/?m) then the boot information will get written to the tape, THEN THE TAPE REWINDS when that is done, and then the pax archive gets written to tape. In this case the pax archive just overwrote the boot information on the tape rendering you m_t_r tape utterly useless.

[D Block 2]

yes, there are multiple files writen to the tape, therefore, no need for rewinds..

btw, the disciple for no-rewind, is an AT&T standard device named: 0mn where 'n' means no-rewind.

so, here's the point from an Ignite tape:

to recover one file from an ignite tape try this one:

skip the 2 files on the tape:
mt -t /dev/rmt/0mn rew
mt -t /dev/rmt/0mn fsr

# so do the rewind, then Forward Skip Record (fsr)

recover a unix file from the tape:

tar xvf /dev/rmt/0m /etc/hosts

# note, this time, you don't need the '0mn'.