time machine behavior, post clone of home disk

[pfile]

hi all,

i've got my home directory on a separate disk from my boot disk, and my home disk is running out of space.

i was planning on using SD! to make a clone of my home disk in order to move to a larger disk. i've got a time machine backup going as well.

in the past i'm pretty sure that time machine has considered a disk upgraded in this manner to be a whole new disk, and therefore it makes a brand new backup. i'd like to avoid this... does anyone have any hints?

i'm thinking that perhaps somehow i have to clone the UUID of the old disk to the new disk. is there anything more that has to be done to fool time machine into thinking the upgraded disk is identical to the old disk?

thanks for any ideas.

[dnanian]

I'd really start a whole new TM backup... I think, in general, it's a mistake to try to 'fake out' Time Machine.

[pfile]

okay... its just that my TM disk is full, and it's probably going to have to delete a bunch of perfectly good backups to make room for another copy of the same thing.

are you speaking from experience here? i know time machine is very complicated... i'm already using it "off label" a bit - i'm backing up to a ReadyNAS that's masquerading as a time capsule...

[dnanian]

I just generally don't believe in doing things that are kind of explicitly unsupported. It's a great way to lose data.

[pfile]

Originally Posted by dnanian

I just generally don't believe in doing things that are kind of explicitly unsupported. It's a great way to lose data.

true. so i guess apple must expect that if you want to upgrade to a larger disk and preserve time machine continuity, you will create your larger disk by restoring it from TM?

[dnanian]

I think they expect you to toss the old data. It's not an archive, after all.

[pfile]

well against my better judgment and (everyone else's ) i used SD! to clone my 1TB disk to a 1.5TB disk and then hacked TM, changing its UUIDs for the disk in question to the new UUID. seems to have worked, i was able to do a new backup and restore some files just fine.

[camner]

Do you mind telling me (us) how you changed the UUID?

After repartitioning my drive (cloning off/on with SD!), TM no longer will backup the drive (fails with an error of type 12, something about not being able to link files correctly). A Google search turns up the fact that when I repartitioned (using the same names for the partitions), the UUID changed, which apparently causes the problem.

dnanian's comment that "it's not an archive after all" is interesting. Isn't TM supposed to be exactly that, an archive, allowing one to restore previous versions of files? He knows far more than I do, of course. What does this mean?

[dnanian]

It means that Time Machine throws away old copies when it runs out of space. It is not intended as an archive, and using it that way will, eventually, result in heartache.

[camner]

Originally Posted by dnanian

It means that Time Machine throws away old copies when it runs out of space. It is not intended as an archive, and using it that way will, eventually, result in heartache.

You are absolutely correct, of course. This is a marked difference than what one would expect in a true "archive."

My experience over the last year with TM is that it is not particularly robust. I've had to "start over" with a fresh TM a couple of times. It seems that TM is best for keeping a current backup continuously to guard against a sudden disk or volume failure that will allow one to restore quickly (hopefully) in case of such a sudden failure. Archiving should be handled differently.