New hard drive Mountain Lion - what to restore?

Question

I am upgrading my iMac to include a 240GB SSD, in addition to the 1TB hard disk already in the machine. I will re-install Mountain Lion from a thumb drive on the SSD. Despite having searched on the web, especially through Pondini's website, I am still unclear about what I SHOULD sendibly restore from my Time Machine backup. There was a lot of no longer required data on my old installation, and I want to keep the new one as clean as possible.
1) I was not planning on restoring Apps, as there are so many that I no longer use. Or is there a good reason to still bring eveything back?
2) User folder - I can select what I need, and most of the docs will need to be restored manually onto the 1TB (as the SSD is much smaller) anyway which is no longer the boot drive. However, if I copy a User folder, I have no choice but bring the User/Library folder across, and looking at this usually hidden folder, it contains a lot of data that refers to apps I am no longer using. Would it be cleaner/better to restore user files manually? Would it mess things up if I brought the User/Library folder across but not the Apps?
3) Settings - should I restore these, or will I have loads of things moved that are no onger useful? I have read that I needed to transfer settings to be able to inherit Backup history, is that correct? Does the back-up history inheritance work anyway, given that the history was created when the 1TB drive was the boot drive.
4) Is there anything else?
Thanks in avance for some views - I am pretty clear on HOW to execute the restore, but I am really noy certain WHAT is sensible in terms of optimizing the future set-up.

Answer 1

HenrikSUefke wrote:
Pondini, thanks. I hate to ask another question but perhaps you have some more patience with a first time restorer, and hopefully many will benefit from the answer:
Actually, this is a fairly unusual one, so it's not the same old, same old. 
My 2TB Time Machine back-up disk is actually full, as I have also backed up a few things from an external drive in addition to the 1TB internal drive. If I inherited the back-up, the external part on the unchanged drive would not get duplicated again, would it
Correct.  Each drive is backed-up and kept separately.
(so I would benefit from the inheritance in some way?)?
Technically, there are two different things:
• Backup inheritance:  An entire set of backups "belongs" to a physical Mac (using a hardware address).  When you get a new Mac and set it up from the old one, or it's backups, Time Machine will start an entirely new set of backups for the new Mac, unless the old ones are "inherited."  Depending on how you moved your data, this may be automatic (the prompt in #B5 of Time Machine - Troubleshooting), or you may have to do it manually (via #B6 there).  It also happens if you get a new logic board in an existing Mac, since that's where the hardware ID is.
• Disk association.  When you erase or replace a drive, it's usually treated as a different one unless it is "associated" with the old backups of a particular drive.  There is no separate prompt for this.  It's done along with the inheritance of a new Mac, but isn't needed when only the logic board is replaced.  We don't usually mention this when talking about inheriting another Mac's backups, as it's included. You can also do this manually, per the pink and/or tan boxes in #B6.
So in your case, you don't need to inherit.  The backups of the external won't be disturbed, space permitting.
Since the SSD is new, it will get a full backup.
Since the HD's folder structure has changed, you can't "associate" its backups.  Well, now that I think of it, you could (and it might not be a bad idea, so you don't need the #E3 workaround), but it's going to get a full backup anyway. 
Time Machine would however have to erase something to get the new SSD and folder structure backed up, so what would that be? Random data from the old drives
No, it will start deleting entire backups, oldest first.  That includes the backups for each drive. Here's the folder structure of some of my test backups:
Lion is the name of the OSX partition; the February backup included an extra partition.  Your existing ones with the HD and external look similar, and all your new ones with the SSD and HD will, too.
However, it will never delete your last remaining backup, for obvious reasons. That's why you need enough room on it for a full backup ofboth drives, plus 25% or so (for workspace, etc.).  If there isn't, the backup will fail for lack of space.
- in which case I guess I would have to be very sure that I restore all data before the first new back-up
If there isn't enough room, and you don't have other backups, I'd strongly recommend biting the bullet and getting another drive.  If something goes wrong, you'll be in a large pickle.
And if you don't have other backups, please consider getting another drive for that anyway.  See Time Machine - Frequently Asked Question #27 for an explanation and some suggestions.  $150 is a lot of money, but is it worth risking your data?
(do I actively have to prevent a back-up, or does it not start automatically?)?
If you did the backup while Time Machine was ON, and transfer Computer Settings, the SSD will have exactly the same setup for Time Machine as the old HD did.  So yes, an hour after you start up, TM will probably try to do a backup.  Either turn TM OFF before doing the last backup manually (via Back Up Now), or turn it off when your Mac restarts after running Setup Assistant.
Or does it erase external data first? Or would it tell me that there is not enough space?
The first thing it does is figure out (estimate) how much it's going to back up, then adds at least 20% (often considerably more) for workspace, then sees if there's room.  If not, it tries to make room by deleting old backups.  If it delets all but the last, but still doesn't have room, the backup fails with the message in the pink box of #C4 in Time Machine - Troubleshooting.
Do I understand correctly that it will not recognize the same files on the SSD or the new HDD folder structure as existing, so it would duplicate them?
Yup, exactly.
There are some ways you might be able to "squeeze" a new backup on to the drive, then selectively delete all the backups of selected items from the old locations on the old backups.  But that will help only if most or all of the earlier backups are deleted, is unlikely to save much space, and would leave some holes in your backup history.  Probably not wise while making all these changes.
So, do some calculating!