How to span multiple 2x sided Magneto-Optical disks for backup?
 

Does anyone have any idea how to span media with tar when using two sided media such as the MO discs? I've used -M to span media on a DLT drive with tar, but that only prompts for new media. As far as I know tar is not intelligent enought to flip MO discs. I'm hoping I can figure something out by specifying the size of the MO disc and then flip it, but I'm not sure how I'd resume backing up from where I left off?

I've already verified I can use the medium via a direct tar backup (tar -cvf /dev/sda /etc) and by making a partition and ext3 fs on one side of one of the MO cartridges as well.

Just because I am curious...

How do you flip an MO disk? I mean, do you have to tell /dev/sda to flip (and how do you tell that) Or do you have multiple devices, say /dev/sda1 for side 0 and /dev/sda2 for side 1?

jlinkels

/dev/sda and /dev/sdb are just the optical drives as block devices, and are unrelated to the actual medium changer. The medium changer is just another scsi device on the internal chain. If you wanted to rotate the medium you add 'invert' into your command.. For example would load medium slot 6, rotate it, and insert it into drive 1. (/dev/sg1 being the medium changer/robot)

But the man pages work best, since that's where I learned it from anyways.

Ok, is it correct that your problem is that tar does not know how to flip the disk?

In that case, use "star". That is a more or less upward compatible "tar". You can get it here

Star offers you an option where you can specify a script name (new-volume-script=script)when the media has to be changed. Since you know what command (mtx etc) you have to issue for changing the disc, you can specify that.

I also wrote this post about star in this forum.

BTW, are you sure that you want to make multi volume backups? If one media fails, you loose everything! On my system, I made all my disk partitions equal to the size of my backup media. So a partition is guaranteed to fit on my media. Restore and verify is MUCH easier and more reliable that way.

Let me know if this was your problem and whether you could solve it.

jlinkels