Time Machine - Troubleshooting

B6.  "Reconnecting"  to  your  backups

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Some situations can cause Time Machine to start a new, full backup when you don't want it to.  On Snow Leopard and Lion:

  1. •You get a new Mac.  If you transfer your data via Setup Assistant (preferred) or Migration Assistant, you'll be asked whether to start a new set of backups.  See item #B5 for details and instructions.

  2. •Your Mac's logic board (motherboard) is replaced.  OSX thinks you got a new Mac, so you'll be asked whether you want to start a new set of backups, as above.  See item #B5.

  3. •You get a new internal HD, or erase your internal HD.  If you transfer your data to it via a full system restore (preferred), Setup Assistant, or Migration Assistant, Time Machine should not do a new, full backup (but on Snow Leopard, sometimes it does anyway).

  4. •You get a new data-only drive, or erase and restore one.


If you got a new Mac or internal HD, or erased and restored your internal HD, but moved your data to it by other methods (such as restoring from a "clone" or drag & drop), Time Machine will do a new, full backup.  Similarly, if you replaced a data-only drive, Time Machine will do a full backup of the new one. On Lion only, you may be able to prevent that in such cases, but it's a bit complicated:

If you get a new Mac and don't transfer your stuff as above (or don't get the prompt in item #B5), you can make your new Mac "inherit" the backups of your old one (unless your backups were made over a network).  You'll need to use the procedures in both the blue and pink boxes below.

If your Logic Board is replaced, and you don't get the prompt in item #B5, you can make your new Mac "inherit" the backups of your old one, per the blue box below.

If you replace or erase your internal HD and don't transfer your stuff as above, you can tell Time Machine to "associate" the backups to the new HD per the pink box below.  This does not work if your backups are on a network.

If you replace or erase a data-only volume  and restore the data, you can tell Time Machine to "associate" the backups to the new HD per the tan box below.  This does not work if your backups are on a network.

These procedures require using the Terminal app, in your Applications/Utilities folder.

Be extremely careful when using Terminal.  It is a direct command-line interface into UNIX, the underpinning of OSX.  Unlike the Finder, there are few protections against making a mistake, which can cause untold damage.

In Terminal, the prompt looks like this:   <ComputerName>:~  <your name>$

(where <your name> is your short user name).  It's followed by a non-blinking block cursor.  When you first start it, you'll see something like this:


      




The commands below are prefaced by the term "sudo" which means to execute the command with "root" or "super user" privileges.  The first time you use it in a session, you'll see some warnings and a prompt for your Admin password (nothing will be displayed as you type your password).  Press Return again.

Normally, there are few error or confirmation messages in Terminal.   When a command completes, you usually just see another prompt.

 

"Inherit" a backup

Copy the following after the prompt, and leave a space, but do not press Return yet:

                            sudo tmutil inheritbackup

If your backups are on an external HD, locate and open the drive in the Finder window.  At the top level of the drive is a Backups.backupdb folder containing a folder named for your old Mac, per the sample.  This is what you want the new Mac to "inherit." Drag that folder to the Terminal window. 

If your backups are on a Time Capsule, locate the sparse bundle containing the backups for your old Mac via the Finder, and drag it to the Terminal window:

                                 

                                   

Terminal will supply the "path" to the dragged folder or sparse bundle (underlined in red):

                                                     

                            

Press Return, enter your Admin password if prompted (it won't be shown) and press Return again.

 

"Associate" an OSX volume

To "associate" the OSX volume you're running from, copy the following after the prompt, leave a space after the slash, but do not press Return yet:

                            sudo tmutil associatedisk -a /

Open the backup drive in the Finder window.  At the top level of the drive is a Backups.backupdb folder containing a folder named for your old Mac.  Inside it is a folder named for your Mac.  Inside that are a series of time-stamped folders.  Inside each of those is one folder for each volume (disk or partition) that was backed-up.  Locate any folder for the "old" volume (the name may be the same as the new one, but Time Machine knows it's a different one).  Drag it to the Terminal window:

                     


Terminal will supply the "path" to the dragged folder (underlined in blue):  

                   

         

Press Return, enter your Admin password, if prompted (it won't be shown) and press Return again.

Note that Time Machine will change the name of the disk on the existing backups to the name of the new one.  In the sample, if the new OSX disk is named Lion, the disk name on all the old backups would be changed from Macintosh HD to Lion.  (That may take a few moments.)

 

As noted above, if you make a mistake with one of these commands, there may not be an error message.  If there is one, it may be in "geek speak," unfortunately.

If done correctly, the next backup should not be a full one, but it will take longer than normal, especially after using the associatedisk verb. 

However, in some cases, especially on 10.7.0, Time Machine may say it's going to do a full backup;  delete a lot of old backups if necessary;  copy data very, very slowly;  but only actually do an incremental backup.  This seems to happen less frequently on later versions.

Note:  these procedures are new with Lion, are difficult to test in many setups, and may or may not work in your particular situation.  For those familiar with UNIX and Terminal, see the man page for the new tmutil command.   Some things that did not work well on 10.7.0 may work on later versions, so use the current version of OSX if possible.

"Associate" a data-only volume (or a second OSX volume)

This is similar to the procedure in the pink box above.  There, the first slash represents the current OSX volume, but in this case, you want the new data-only or second OSX volume.

Copy the following after the prompt, leave a space after the -a, but do not press Return yet:

                            sudo tmutil associatedisk -a 

From a Finder window, drag the new disk/partition to the Terminal window.  It will supply the path as above.  If it's not followed by a space, add one, but do not press Return yet.

Now follow the instructions in the pink box to drag the old volume from the Finder window containing the backups to the Terminal window, and press Return.  The final command should look something like this (the new second drive is "NewDataDrive", underlined in green;  and the backups of the old one were on "DataDrive", underlined in blue):


As in the pink box, if the disk names are different, Time Machine will change the old name on the backups to the new one.  (That may take a few moments.)

 

Before starting:   Log on as an Admin user, and make sure the backups in question are connected to your Mac.

Select them as your backup destination via Time Machine Preferences > Select Disk, but immediately turn Time Machine OFF so a backup won't start.

Open a Finder window to the backups, preferably in List view, and leave it on the screen, as you'll be dragging things from it into the Terminal window below.