Time Machine - Troubleshooting

C13.  " . . . Time Machine must create a new backup for you."

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This extraordinary and rather scary
message means Time Machine has found some sort of problem with your network backups, something that Disk Utility can’t find, much less repair.

This verification, and message when it fails, started in 10.6.4, released in mid-May of 2010.  It's usually run automatically, once a month.  You can also run it manually, by holding the Alt/Option key while selecting the Time Machine icon in your Menubar and selecting Verify Backups.

It’s covered in this Apple article:  If you see a message that you must create a new backup.


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You may find some instructions on the Internet about repairing and "reconnecting" to these backups, instead of letting Time Machine start a new set.  That may even appear to work.

But that does not mean your backups are intact.

Technically, if the "repair" uses the fsck UNIX command with the -y option, it may not really fix anything.  According to the manual page about that option:  "this should be used with great caution as this is a free license to continue after essentially unlimited trouble has been encountered."  That means any missing or damaged files may be deleted, but the command completes normally (where Disk Utility will fail with the red "could not be repaired" message.

Thus, you don't know what or where the damage is, and you may not detect it until much later, when you can't find or restore something, or your backups are useless.

Especially if these are your only backups, not believing the message is very risky.

Possible Causes

If this happens frequently, check for these problems:

  1. Network problems:

  2. See  AirPort and Bluetooth: Potential sources of wireless interference for possible network problems, especially interference.  Use the free  iStumbler  app to examine the strength of your connection.  You may want to move your Mac and/or router around to find a location that will improve the signal quality.  Of course, if interference is intermittent, it can be very hard to pinpoint.

  3. Power problems

  4. What power source is your router (and/or the destination for the backups) plugged-in to?  Could there be power spikes or dips?  Some are so quick you don't notice your lights dimming, but can cause all sorts of trouble, including directory problems on your backups.  Consider getting a small U.P.S. (battery back-up) system for them.

  5. Names

  6. As odd as it seems, the names of some things may be a problem.  See item #C9.

  7. Hardware failure

  8. It's possible your router, or the drive you're backing-up to, is beginning to fail.

  9. Time Capsule firmware

  10. If you're backing-up to a Time Capsule (or a USB drive connected to one), be sure it has the most current firmware, via the Airport Utility app.

  11. NAS Incompatibility

  12. If you're backing up to a NAS (Network Attached Storage) disk, use the widget in section #A1 to look at the backup messages in your logs.  If you find these:

  13.     Warning: Destination <backup drive> does not support TM Lock Stealing

  14.     Warning: Destination <backup drive> does not support Server Reply Cache

  15. your NAS is not fully compatible with your version of Time Machine.  Contact the maker of the NAS for an update.

  16. Even if you don't see those messages, it's possible your NAS isn't entirely compatible with Time Machine on the version of OSX you're running (the requirements sometimes change with new versions of OSX).  Check with the maker.


If you can't find a solution in a reasonable time, you need to find a way to make reliable backups.  There are two basic choices:

  1. Back up with Time Machine to a more reliable destination.  See Time Machine FAQ #2.

  2. Back up to the same hardware with a different backup app.  See the green box in Time Machine FAQ #27 for some suggestions, but note they don't all work over a network.  If you're using a NAS, some makers have backup apps of their own.

You may also want to report the problem to Apple.  See Reporting a problem to Apple.

If you're using a NAS, also report it to the maker.  Many (perhaps most) cases of this seem to be the result of incompatible or inadequate software on the NAS.

Time Machine locks the sparse bundle containing your network backups, and marks it as damaged.  It may also change it's name to <computer name>.purgeable.  You may be able to view and restore some things from these backups, but you will not be able to continue backing-up to them.  Disk Utility may appear to repair them, but they’re still damaged and if you try to back up to them again, you’ll just get the same message again.

If you select Back Up Later, you'll see the message again in 24 hours. Time Machine will not perform backups during this time.

If you want to try to "archive" the damaged backups before they're deleted:

  1. If your backups are on an AirDisk connected to a Time Capsule or Airport Extreme;  or a shared drive on another Mac; or a NAS (Network drive) you probably won’t be able to  copy them as detailed in Frequently Asked Question #18, since Time Machine has already marked them as corrupted.  In that case, you’ll have to either erase them or use a different drive or partition for the new backups.

  1. If your backups are on a Time Capsule’s internal HD, see the green box in  #Q6 of Using Time Machine with a Time Capsule.  The "archived" backups will still be marked as damaged, but you may be able to view and restore some things from them.

If you select Start New Backup, Time Machine will delete all the backups of this Mac (leaving any others, and any other data, on the backup disk alone) and create a new set starting with a full backup of your entire system.  That will take a long time, so:

If there's nothing else you need on the backup disk, it will be much faster to just erase it, rather than have Time Machine delete the sparse bundle:

  1. For backups on a Time Capsule's internal HD, use Airport Utility, per the green box in #Q5 of Using Time Machine with a Time Capsule.

  1. For backups on an external HD connected to a Time Capsule or another Mac on your network, connect the drive directly to your Mac and erase it with Disk Utility, per #1 in Using Disk Utility.

  1. For backups on a NAS (Network Attached Storage, or Network drive), use the windows provided by the maker.

If you do let Time Machine delete the old backups, there's a small chance the sparse bundle is so damaged it can't even delete it.  If so, you'll get a message to that effect, and you won't get all the space back.  If there's nothing else you need on the disk, erase it as above.  If there is, try to delete the sparse bundle yourself.  If it's on a Time Capsule's internal disk, see the tan box in  #Q5 of Using Time Machine with a Time Capsule.  If it's on a NAS, you may have to use the facilities provided by the maker.  If it's elsewhere, try to delete it via the Finder.

Since it's a periodic verification of prior backups, it doesn't indicate what caused the problem, nor when it occurred -- just that it was since the last successful verification.  That makes it rather difficult to find the culprit.  See the pink box below for some possibilities.