Q: My back up drive has more data than my computer

For the future:  You have posted your question in the "Using Apple Support Communities" community - and your question is not about using the community - it is about how to manage disk space on your Mac and backup drives.  You will get quicker and better responses if you repost your question in the Mac OS X and System Software community.  Please don't post the same question in multiple communities unless someone has indicated you have posted in the wrong community.  Before you post - make sure to select the correct community at the bottom of the post.  I don't believe that it is possible to move a post to a different community.

~Scott

I am having our Hosts move this to Yosemite forum as we speak

Hi Helen,

You have indicated that your external drive is being used with Time Machine.  When you use an external drive with Time Machine - the drive becomes somewhat dedicated for use exclusively by Time Machine.  It is not a good idea to attempt to store non-backup data on the Time Machine drive - and it would cause problems if you were to attempt to delete any files or folders on the drive because you would risk corrupting your backup.  Time Machine attempts to use all available space on an external drive - and when the space becomes considerably low - Time Machine will start cleaning out older backups to make space for new.  This can slow down the Time Machine backup process.  It is very possible (and expected) that your backup drive will eventually contain more data than what currently exists on the Mac's internal drive - because the backup drive is keeping historical backups.  This is normal.

Please indicate the size of your external backup drive?  I'm assuming that it is at least 1TB?  I will attempt to provide a more optimal solution once you provide this information.

~Scott

Guessing at what you're looking to do: Easiest way is either adding disk storage, or using a network file transfer.

In general (and as some background)...   If you want to restore to the new Mac from Time Machine, then restore from Time Machine.   Pondini aside, I'd expect altering the contents of Time Machine may well corrupt the archive, and would not recommend experimenting with your sole backup in any case.   If you don't have enough external storage, you can choose to delete the Time Machine archive, or restore it to your new Mac and then delete the archive.  That also obviously nukes your archive.   If you still don't have enough storage (or don't want to risk or damage or corrupt or delete or otherwise lose your backups), acquire more — 4 and 6 TB drives and larger are now available, which makes the remaining 1 TB drives less expensive.   If you don't want to acquire a new drive, then use some other means — Ethernet would be common — and transfer the files that way.

To use the Network File Transfer between the two systems, connect to the same Wi-Fi or wired Ethernet network, and use  > System Preferences > Sharing to enable file services, then from the other system find the other and mount the share using Finder, and drag the files from the old system to the new system via Finder.

Time Machine archives — if they're current — can be used for the migration.

Migration Assistant can select groups of items — Apps, or Documents, for instance — but AFAIK can't exclude specific items; it is a very blunt weapon for deleting specific apps.   Either delete those items at the source Mac prior to the transfer, or delete those after the transfer.

FWIW, if your backup consists of Time machine backups, then I'd guess that TM is simply doing what it is designed to do: at some point, it made a full first backup, and since then, it has made incremental backups. It does that until it runs out of space. At that point, it will delete the oldest backup to make room for a new one.

Your TM disk should always be at least 2 - 3 times the size of your internal disk.

If you wish to restore your files to a new Mac, you can simply choose which backup you want to use in TM. Here is some info:

http://pondini.org/OSX/SetupLion.html

http://pondini.org/TM/FAQ.html

http://pondini.org/TM/14.html

Getting the new 2TB drive is a good start as you will have more flexibility.  Can you clarify a couple of things?

1.  Are there actually two Mac's and old and a new?  Or is there only one Mac - the new one? Which Mac has the 1TB internal drive with 500 gig already used - the old or the new?

2.  Was your original external drive used "only for Time Machine" or were you also storing important files on it along with the Time Machine backups?

You should definitely use the new 2TB external drive for Time Machine.  You could conserve some of the space on the new 2TB drive by partitioning it into 2 1TB drives.  If you choose to do that - it would need to be done "before" using the new drive for Time Machine.  Time Machine would use only one partition for the backups - which would not exceed 1TB - and you would have a 1TB "data" drive to use as a workspace - but keep in mind that the only files you should be storing on the external drive should be files that you don't care about losing - as they are not being backed up to anything.  If you decide later that you want to allocate more than 1TB to Time Machine backups - you can resize the partitions without losing data on either (assuming there is enough free space to resize).

~Scott

Ok - that makes things clearer.  If you choose to move files to the new Mac using Migration Assistant by "transferring from a Time Machine backup" - the actual amount of data that will be transferred will probably be significantly less than the amount of space showing as in-use on the backup drive (with only 80 gig remaining) that you are transferring "from".  I think you will be okay.  Just be sure that you aren't trying to manually or selectively copy files or folders from the backup drive - as those can only reliably be copied by Migration Assistant or via a Time Machine restore.

~Scott

A Time Machine restoration or Time Machine migration will be about the same amount of storage as on the source disk.

About the same?   Total storage requirements will likely be somewhat larger after the restoration — probably on the order of several gigabytes or so — as the decade-old Mac will probably be on an older OS X release, and the newer OS X releases and newer tools and apps are usually a little larger.  What will be a negligible difference, with most configurations.

You won't get the now-gone files and the change history and the rest from the historical data present in the Time Machine archive, you'll get a current copy of the most recent Time Machine capture from the source Mac.