Strange Time Machine behavior in ML

ungar · Feb 20, 2013

In previous versions of OS X, when my Time Machine backup disk (external USB) wasn't connected and it was time for a scheduled backup, no backup was made, and that was that. Now, with Mountain Lion, I get an dialog saying that the identity of my backup disk has changed, would I like to backup to the new disk? And the "new" backup disk is none other than Macintosh HD. This is weird behavior in my opinion. Any way to revert?

Thank you

Edie Brickell · Feb 22, 2013

This is absolutely weird as how can you backup your data on the same drive from which you want to take backup. There is some problem with your time machine or selection of drives. Choose an appropriate drive to backup your data.

switon · Feb 24, 2013

RE: Time Machine and local snapshots...

Hi ungar,

Time Machine running on a laptop will backup to your specified backup volume when it is attached. When your TM backup volume is not attached and cannot be mounted, then TM by default makes what are called local snapshots. These are TM differential backups stored locally on your boot disk.

You can disable local snapshots using the "tmutil" terminal command:

Code:

sudo tmutil disablelocal

Or reenable local snapshots using:

Code:

sudo tmutil enablelocal

Or you can even instruct Time Machine to make a snapshot using:

Code:

tmutil snapshot

Note: If you switch off TM and switch it back on, then TM's behavior reverts back to the default, that is, it will automatically make local snapshots.

I don't think this is your problem, however, as TM should not have asked for a new backup disk just to make local snapshots, as local snapshots are, by default, stored on the boot disk. This is a laptop, right? If it is not a laptop, then all bets are off, and I suspect that TM will indeed ask if you wish to use a new backup volume if you disconnect its current backup volume. (I suspect that you can force TM even on a non-laptop to make local snapshots using the above "tmutil enable local" command - but I haven't tried this.)

Regards,
Switon

ungar · Mar 1, 2013

Hello Switon,

I don't think that is the problem either. I was alterted to the problem in the first place when I found a backups.backupd folder directly under my Macintosh HD, not in the Mobilebackups folder where the local snapshots are kept. Be that as it may, I have disabled local snapshots, and will see what happens. Thank you.

ungar · Mar 1, 2013

Indeed, I disabled local snapshots, but I'm getting the same strange "backup disk identity changed" dialog. Any ideas?

thank you

switon · Mar 2, 2013

RE: TM destinations...

ungar said:
Indeed, I disabled local snapshots, but I'm getting the same strange "backup disk identity changed" dialog. Any ideas?

thank you

Hi ungar,

Do a:

Code:

tmutil destinationinfo

in order to see where TM is backing up to. In my case, the above command reports:

Code:

MyMBP:/ myusername$ tmutil destinationinfo
====================================================
Name          : SC-MyPassport-2TB-04-TM
Kind          : Local
ID            : D90A49CE-8A54-454F-A407-XXXXXXXXXXXX
====================================================
Name          : SC-2TB-03-TM
Kind          : Network
URL           : afp://myusername;AUTH=SRP@mytc._afpovertcp._tcp.local/SC-2TB-03-TM
ID            : 2DE05C1D-1CBC-44D7-AA66-XXXXXXXXXXXX
> ==================================================
Name          : myusername
Kind          : Network
URL           : afp://myusername;AUTH=SRP@mytc.local/myusername
ID            : 0CEBE3A8-9D95-42C3-B10F-XXXXXXXXXXXX

where I have obfuscated my name and computer's name, and my Time Capsule's name for security reasons. Notice that when I backup over the network (both to my TC and to a USB disk plugged into my TC), TM mounts via AFP and authenticates to "myusername". On the other hand, when I backup to a local external USB drive, no authentication is required. Check you TM destination(s) to see if they are copacetic in comparison to mine. Are you backing up to a local or network drive? If it was a network drive, did you change your username, computer name, or the name of the volume on the other computer mounting the drive?

It may be that all you need to do is just reset the destination for you TM to the correct drive. (And you may never know why or how TM forgot its destination in the first place.)

Regards,
Switon

ungar · Mar 5, 2013

Thank you switon; I really appreciate your efforts to help me out.

Right now, my usb backup drive is disconnected. When I run the destinationinfo command, I get my (disconnected) drive's name. And yet, when I go into Time Machine preferences, the name of my backup drive is Macintosh HD!! Take a look at the screenshots (my backup drive is called "something", obviously).

Weaselboy · Mar 5, 2013

ungar said:
Thank you switon; I really appreciate your efforts to help me out.

Right now, my usb backup drive is disconnected. When I run the destinationinfo command, I get my (disconnected) drive's name. And yet, when I go into Time Machine preferences, the name of my backup drive is Macintosh HD!! Take a look at the screenshots (my backup drive is called "something", obviously).

Can you try turning TM off, then turn it back on and click select drive and pick the external USB drive. See if it remembers the selection after doing that.

ungar · Mar 5, 2013

Yes, I've done that, to no avail. The point it, Time Machine has no trouble remembering my external backup drive as long as it's connected, but when it's not, it changes to Macintosh HD. (I've also tried trashing the preferences, by the way. Nothing works.)

Weaselboy · Mar 5, 2013

ungar said:
Yes, I've done that, to no avail. The point it, Time Machine has no trouble remembering my external backup drive as long as it's connected, but when it's not, it changes to Macintosh HD. (I've also tried trashing the preferences, by the way. Nothing works.)

Do you have Time Machine encryption turned on by any chance? I know that looks odd because it makes an encrypted bundle called Macintosh HD.

switon · Mar 5, 2013

RE: turning TM off/on...

Hi ungar,

There could be a minor difficulty with switching TM off and then back on using the System Preferences TM pane. That difficulty is that TM may then wish to "begin anew", and make a new backup from scratch. If this occurs, then you can get around this by using the "setdestination" or "inheritbackup" options of the "tmutil" command. Root privileges are required.

So, let me understand...when your external backup drive is attached, then TM will make differential backups to it. When your external backup drive is not attached, TM makes differential backups to a sparsebundle on your boot drive. You have local snapshots disabled. Your "tmutil destinationinfo" command returned only what you included in your attachment. --- well, this has me stumped, let me think about it further. (By the way, this is not in my experiences how TM operates.) Sorry for the lack of help.

Switon

Weaselboy · Mar 5, 2013

switon said:
When your external backup drive is not attached, TM makes differential backups to a sparsebundle on your boot drive.

I know you can set two drives as backup destinations and they alternate... it almost sounds like he selected both the external and also Macintosh HD as backup destinations. But wouldn't the "tmutil destinationinfo" command show that? I'm a bit baffled here too.

switon · Mar 5, 2013

Weaselboy said:
I know you can set two drives as backup destinations and they alternate... it almost sounds like he selected both the external and also Macintosh HD as backup destinations. But wouldn't the "tmutil destinationinfo" command show that? I'm a bit baffled here too.

Hi Weaselboy,

Yes, the "tmutil destinationinfo" would show this, as you can see in the output I included in my earlier posting, I use three separate drives for TM backups, two are networked drives and one is an external USB3 drive, and all three of these drives show up in the "tmutil destinationinfo" output. This is why I'm stumped...it appears that TM does not know about any other backup except for the OP's external drive, and yet according to the OP TM still makes differential backups to his/her boot drive when the external is not attached. This behavior is not what I experience, and I don't think that this is proper behavior. I must be missing something here.

Regards,
Switon

switon · Mar 5, 2013

RE: I wonder if...

Hi ungar,

I wonder if it could have something to do with the fact that your TM thinks the external drive is mounted under "/" and not the more typical "/Volumes"? In other words, when you mount the external backup volume, it should mount as /Volumes/<backupvolumename> instead of /<backupvolumename>, or when TM starts it should be mounted as /Volumes/Time Machine Backups. Is the tmutil destinationinfo lying to us, or does your external drive actually mount as /<backupvolumename>?

As you can see in my tmutil destinationinfo output, my mounts points are not even listed, probably because they are standard /Volumes mounts.

If I were you, and I know you probably don't want to hear this, I'd abandon this TM sparsebundle and start over, setting up TM once again to backup to an external volume that is mounted under /Volumes.

Regards,
Switon

P.S. And when my external drive is mounted for TM backups, then the tmutil destinationinfo returns the drive as being located at /Volumes/<backupvolumename> while your destinationinfo indicates a mount point of /. When your external volume is actually mounted and TM is backing up to it, does tmutil destinationinfo show /Volumes/<backupvolumename>, or does it show /<backupvolumename>?

ungar · Mar 5, 2013

Dear switon,

Now that's interesting. To answer your last question, when my external HD is mounted, I indeed get /Volumes/ as its mount point (see screenshot). Then, when I unmount it and run the destinationinfo command, I get the same result as above. So, since my external HD seems to be mounting correctly, I'm reluctant to erase it and start over.

With regard to another question you ask, whether TM makes differential backups to a sparsebundle on my boot drive when my external HDis unmounted, I think the answer is "yes", since, at one point, I noticed a mysterious Backupsbackupd folder directly under Macintosh HD, which I deleted, and, ever since, when I get the dialog saying that my backup disk's identity has changed, do I want to back up to the new destination?, I always refuse.

Weaselboy · Mar 5, 2013

Ungar-- I noticed a couple threads in the Apple Support forums with people having the same problem. In this thread it was fixed by shutting down TM, then erasing the external and starting over.

The symptoms described in that thread are exactly like yours.

switon · Mar 5, 2013

Ungar,

So, to summarize, when TM is backing up tp this external volume, then tmtuil destinationinfo returns /Volumes/<backupvolumename>.

Fortunately Weaselboy has found the same problem in the Apple Support forums, but the solution listed there is the extreme and somewhat unsatisfying "start over". But I always worry that the problem will happen again unless I understand why it happened in the first place, which is why I try to fix these problems instead of just starting over.

Good luck,
Switon

ungar · Mar 5, 2013

Indeed, Weaselboy, that is the same problem as mine. I'll see if I can go on living with it (I turn Time Machine off when I'm on the road without my external HD in order not to get those annoying dialogs), and reformat if I get fed up. In the meantime, I'll stay tuned to this thread in case someone comes up with something. Thanks switon and Weaselboy!

switon · Mar 6, 2013

RE: Turning TM off...

ungar said:
Indeed, Weaselboy, that is the same problem as mine. I'll see if I can go on living with it (I turn Time Machine off when I'm on the road without my external HD in order not to get those annoying dialogs), and reformat if I get fed up. In the meantime, I'll stay tuned to this thread in case someone comes up with something. Thanks switon and Weaselboy!

Hi ungar,

After reading the Apple Discussions thread which Weaselboy found, it makes me wonder if this problem stems from or is initially caused by turning off TM at an inopportune time. Perhaps a drive was dismounted while the TM software was in the initial phases of starting a TM backup, so without the backup volume the software defaulted to / on the boot drive. Or perhaps the TM software was in its initial phases when the user decided to switch it off, and in its initial phases it begins with setting the backup volume to / on the boot drive (default) before resetting it to the actual backup volume specified in the preferences. But the TM software never got around to resetting the backup volume since it was switched off. Those familiar with the actual TM code could tell us this. And once reset to /, this default / backup volume, which does not appear in the destinationinfo because it is the default, is employed whenever TM starts without its normal backup volume attached, that is, TM always has a backup volume, the /. You will notice that in my destinationinfo when my external backup volume is not attached, then destinationinfo does not list a mount point at all, but in your destinationinfo when your external drive is not attached, then a mountpoint of / is listed.

Instead of "starting over" with a new TM backup, what if you first do a "tmutil removedestination" to remove the external volume with its associated / mount point. Then do a "tmutil setdestination" to add back your external volume? Would this work? It's discouraging that the only solution is to start over, and that nobody seems to know what causes this error in the first place.

Regards,
Switon

ungar · Mar 6, 2013

Too late; I decided there was nothing on my backup volume I really needed, so I reformatted and am now in the process of running a new initial backup. At any rate, when the disk was unmounted, destinationinfo was returning "something" as my backup volume, not / . / was the mount point.

I will see whether the problem reoccurs after starting afresh and will keep you posted. Thanks again.

ungar · Mar 6, 2013

The backup is finished, and destinationinfo is returning the right info when the external is both mounted and unmounted. In a way, it's reassuring; I was at first afraid the problem was normal behavior for ML, as though my computer, in the absence of a mounted TM volume, was trying to back up the the next available mounted volume, i.e., my Macintosh HD. Since the problem arose shortly after the upgrade, that seemed like a plausible explanation. Thanks again switon and weaselboy.

switon · Mar 7, 2013

ungar said:
Too late; I decided there was nothing on my backup volume I really needed, so I reformatted and am now in the process of running a new initial backup. At any rate, when the disk was unmounted, destinationinfo was returning "something" as my backup volume, not / . / was the mount point.

I will see whether the problem reoccurs after starting afresh and will keep you posted. Thanks again.

Hi ungar,

Yes, I understood that destinationinfo was returning "/<something>" and that "/" was the mount point. Sorry if I was confusing in my response. Good luck with your new TM backup. If you ever figure out what happened, let us know.

Switon

P.S. I would turn TM on/off...just leave it on and when your external drive is attached TM will backup to it.

ungar · Mar 7, 2013

Hello switon,

Yes, now that the problem is fixed, I'm leaving TM on all the time. No problem. By the way, may I ask, in case the problem reoccurs, how I use the tmutil setdestination command that you suggested?

switon · Mar 7, 2013

RE: tmutil setdesitination ...

ungar said:
Yes, now that the problem is fixed, I'm leaving TM on all the time. No problem. By the way, may I ask, in case the problem reoccurs, how I use the tmutil setdestination command that you suggested?

Hi ungar,

The "tmutil" command is well documented in the manpages: "man tmutil". The

Code:

tmutil setdestination -a afp://myusername;AUTH=SRP@mytc._afpovertcp._tcp.local/share

would add a new destination (the -a switch) to the current list of backup volumes, an AFP volume authenticated to your username on mytc. Of course, you would have to specify whatever AFP share you use for your backups, or whatever external drive you use. I also would look into the "tmutil inheritbackup" command, as you will probably need both.

Regards,
Switon

ungar · Mar 7, 2013

Thank you switon.

Strange Time Machine behavior in ML

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