Time Machine - Troubleshooting

D1.  Stuck in "Preparing"  or  "Calculating changes"

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The first question is, "How slow is slow?"  Some backups will be faster than others, for a wide variety of reasons, even on the same hardware.  See Time Machine FAQ #29 first.

Time Machine backups can be very slow if your Mac is indexing your internal HD (and/or other drives being backed-up) at the same time.  Click the spotlight icon at the right of your menubar to see if indexing is in progress;  if it is, either cancel the backup, or be extra patient, until the indexing is finished.


Normally, Time Machine can determine what’s changed and needs to be backed-up very quickly, via the hidden log of changes that OSX keeps on each disk.  When it takes a long time, Time Machine may be doing a "deep scan,"  because it can’t use that log for some reason.


Note:  this phase of a backup is called "Preparing" ("Calculating Changes" on Snow Leopard 10.6.x).  They do the same thing;  the only real difference is, effective with 10.6.3 through 10.6.8, you’ll see a "Scanning nnnn items" message on the Time Machine Preference window and/or the small display when you click the Time Machine icon in your menubar, then a "Preparing xxxx items items" message.  That way, the increasing counts in the message at least let you know it’s not "stuck."


You can verify this via the messages in your logs.  See item #A1 for an easy way to do that.


If you see a message there about  ". . . deep scan . . ." on Lion 10.7.x or later, or " . .  . node requires deep traversal" on earlier versions of OSX, that’s what’s going on.


If so, see this Apple Support document: Time Machine may display "Preparing" for a longer time and/or the blue box in section #A6 for details and common causes.  The amount of time required for this is very hard to predict;  it depends mostly on the number of items on your system (rather than the total size) and the connection to your backup volume.  So if you’re backing-up over a network, it’s going to take much longer than to a FireWire 800 external disk, for example, just as the actual backup will.


Try not to interrupt the backup, as this procedure must be done again (and again) until a backup is completed successfully.


Also see the next topic, item #D2.


But if it continues for a very long time, and never starts the copying "xxx MB/GB of yyy GB" messages on the Time Machine Preferences window, something may be wrong with the preferences file.  Cancel the backup (if it doesn't cancel within a few minutes, see item #D6). 


Then try a "full reset" of Time Machine, per item #A4.


On occasion, just Restarting your Mac may clear it up.


If that doesn't help, there may be a directory problem on your internal HD, another disk/partition being backed-up, or your backup volume.    Then Verify your internal HD, and Repair any other volumes being backed-up, and your backup volume, per item #A5.



If you see this frequently, without a good reason, something is probably wrong;  try to figure out which of the reasons in the blue box of section #A6 applies.  If you can’t, post a new thread, with full particulars,  including the messages from the widget, in the appropriate Apple Discussions forum:

Mac OS X v. 10.8  Mountain Lion

Mac OS X v. 10.7 Lion

Mac OS X v. 10.6 Snow Leopard   

Mac OSX v. 10.5 Leopard   

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