Time Machine: The identity of the backup disk has changed since the previous backup

Discussion in 'OS X Mountain Lion (10.8)' started by Dorv, Dec 10, 2012.

  1. Dorv macrumors regular

    Feb 11, 2008

    I have a rather straighforward setup:

    In my office at work I have a Airport Extreme that has a 500GB USB hard drive called Chimeara. It is the only disk I've ever had plugged into this machine with that name. I have Time Machine set to backup to this disk.

    Four times in the last year, I've received the "The identity of the backup disk has changed since the previous backup." When I select "Use this Disk," Time Machine starts a brand new backup, ignoring the previous ones.

    So now I have four old backup bundles, and Time Machine wants to start a new one. Not only am I out of space on the disk (and don't want to delete previous backups), the data I have backed up is fragmented by date making looking for a specific file a major pain in the rumpus.

    Anyone have any guidance on what is causing this?
  2. r0k macrumors 68040


    Mar 3, 2008
    Sorry I don't know what's causing it but I consider a current backup to be infinitely more important than the ability to "roll back" to an 18 month old file. This means that in the roughly half-dozen times I've run into issues with my TM backup for various reason, I've cheerfully deleted the old backups and started over again.

    And deleting the old backups is sometimes a bit tricky. I've had times where the old sparsebundle file didn't want to allow itself to be deleted and I had to resort to a more brute force method like reformatting the disk that contained the thing.

    I should also add that there were 2 events where TM failed to restore data for me. Once my daughter's Mac mini crashed while my Time Capsule was back at Apple for repair and when it came back empty, her files were gone forever. The second was when my wife's files were gone because of a "corrupt sparsebundle." I simply deleted the thing and restored her machine from Crashplan. Thank God I started using Crashplan as a second safety net. The bottom line is that no single backup strategy should be your only backup strategy.
  3. switon macrumors 6502a

    Sep 10, 2012
    RE: now here is a problem...

    Hi Dorv,

    Sorry to hear that you've created 4 different sparse bundles for your TM backups of a single disk. Sometimes TM thinks that the original backup disk is not available. If you are backing up to an attached external drive, then if you attach a different drive with the same name, this will confuse TM. But it sounds like you were using a networked backup drive attached to your AE. In this case, if your network has changed, then TM will get confused and think it can't reach its backup disk. For instance, sometimes my DNS server will die unexpectantly and then I have to refer to various machine by their IP addresses (e.g., instead of by their DNS hostnames (e.g. myserver.private). If TM tried to start a backup when this DNS problem was occurring, then TM gets confused and can't find its backup disk. If you aren't running your own DNS server but are using DHCP to assign LAN IP addresses, then are you using DHCP with Reservations so that machines and networked disks have the same IP address always? If not, then if the IP addresses ever change TM will get confused.

    So, do you have other external disks with the same name? If so, I would recommend changing the names so that all disks have unique names. If you are running your own DNS server, check that it is working properly. If you are assigning your own LAN IP addresses using DHCP, make sure you use Reservations to assign IPs consistently to the same machines and network drives.

    Now to solve your 4 sparse bundle problem. It is possible to redirect where TM restores its files from a given sparse bundle. Thus, in theory, you could use TM for sparse bundle 1 and restore to disk 1, sparse bundle 2 restored to disk 2, bundle 3 to disk 3, and sparse bundle 4 to disk 4. You now have four files systems (really time-dependent copies of the file system on your computer) on four different disks. You could then, in theory, use some tool, like rsync, to merge these file systems into one file system with all of the latest copies and all of the past files that are currently deleted. You could then make a sparse bundle from this pseudo-merged single filesystem that then retains old deleted files. Use this sparse bundle for all future TM backups. It's not perfect, but at least you haven't lost file that you have deleted in the past. It's not perfect because you only are keeping the latest revision of your modified files, not all revisions.

    With a lot more work, you could even keep all revisions of all of your files, but for this I would use the following strategy: (1) restore your oldest TM backup from your first sparse bundle to a clean external disk. (2) Make a git or subversion repository of this filesystem from your oldest TM backup. (3) Restore the next oldest TM backup to the same external disk filesystem. (4) Commit this restore to the git or subversion repository -- this keeps the older revisions of files as well as their histories. (5) Continue this scheme of TM Restore, git/subversion commit, TM Restore, git/subversion commit until you have progressed through all 4 sparse bundles to the "Now" TM backup. Your git/subversion repository will now contains the full revision history of everything in your four TM sparse bundles. If you ever need to go back in time to a previous version of some file, then use the git/subversion repository to find and restore that earlier version. Continue to use your latest sparse bundle for future TM backups.

  4. Dorv thread starter macrumors regular

    Feb 11, 2008
    Yeah, all my critical data lives on Dropbox as well as being backed up on my MBP's Time Machine backup (Come to think of it, that same Dropbox folder is backed up on a Time Machine drives for my computers at home, too).

    I was just hoping there was a way to avoid this happening. I'd rather have one big happy backup, as I have data (email specifically) that I've left archived, but I guess I'm going to have to pull it out and start over.

    I just hate that every time it happens, it takes about a day and a half for the full backup to sync, which kills my Parallels VM I have running.
  5. blueroom macrumors 603


    Feb 15, 2009
    Toronto, Canada
    Consider getting a Synology NAS. Excellent TM backup & much more. Works great with the AirPort Extreme.
  6. Dorv thread starter macrumors regular

    Feb 11, 2008
    Not opposed to anything, but it doesn't look like the media is the issue here as much as the AX.

    What's the advantage of using a Synology NAS in a AX in this case?
  7. r0k, Dec 11, 2012
    Last edited: Dec 11, 2012

    r0k macrumors 68040


    Mar 3, 2008
    I have gigabit ethernet between my Mac and my TC/USB drive so it takes less than 24 hours for me to be up and running with a fresh ~200 GB TC backup.

    Parallels? Every time somebody loads Windows on a Mac, a little kitten dies. :(

    I have Synology, AX and TC. The AX and TC are not ready for prime time in my opinion. The Synology drive is an ARM based Linux box with excellent performance for file sharing and you can run your apache/php web site including wordpress, joomla, drupal, etc from the thing if you want to.

    For one thing, the TC has internal drives. If there is a problem, you mail all your data off to Apple and it comes back empty. The AX is a better solution because you are using a usb drive for data and if there is a problem with the AX, your data never leaves your house. But I'm really not a huge fan of the whole "my router is my NAS" scenario.

    So what I have today is this: AEBS (which I referred to as AX above) which acts as router only. I was getting spotty wifi so I switched off the AEBS wifi. My TC is providing wifi in bridge mode and I ignore the internal drive and use a usb drive for my TM to TC backups. I've heard and have had some experience which seems to confirm that the TC caches OSX updates. My first update is slow but subsequent updates are so fast they seem to be "cached" which is what I've heard the TC will do automatically.

    BTW, I do NOT use TM with my Synology drive. I suppose I could but I'd rather run TM backups to an HFS+ formatted drive and the Synology NAS uses a Linux filesystem (as do many other 3rd party NAS boxes).

    Several advantages of the Synology for me are: (1) BYOD (Bring your own drive), (2) DLNA (media server) and (3) and low power consumption. By putting in a WD green drive, the thing uses less than 18 watts when running and 6 watts in standby. That saves about $100 a year in electricity (estimated) versus running some Linux distro on an old PC chassis for NAS. It is also less power hungry than running an old Mac mini as an NAS box / airplay server. On the Synology, I get DLNA and can stream audio, video and photos while staying within that 18 watt power budget I mentioned earlier.

    If the Synology NAS ever breaks, I can replace the NAS box, pop in my old drive and keep on running. If the drive ever crashes, I can swap it out, put in another one and restore it from a second NAS box I have mirroring the first one. I don't bother with RAID. I'd rather have a completely separate redundant NAS box. There are many utilities available for Unix and OSX to automatically sync two folders so with minimal effort I keep one box looking almost exactly like the other one just in case either one croaks.
  8. Dorv thread starter macrumors regular

    Feb 11, 2008
    If Microsoft would be so kind as to provide us Mac users with Access, that wouldn't be a problem for me ... Until that, though, I'll have Parallels on my machine.

    Your setup sounds great, but its waaaaay too much for my needs.
  9. r0k macrumors 68040


    Mar 3, 2008
    Did I mention the concrete data bunker and my own hydroelectric plant for power backup?
    Just kidding. :D

    I am a tinkerer so I always have more stuff than I absolutely need. If I were starting from scratch, I'd probably still have 2 NAS but I certainly wouldn't also have a TC.
  10. dmmaus macrumors newbie

    Dec 26, 2012
    Sydney, Australia
    I got this error for the first time today. I'm using a 2012 iMac with a Time Capsule plugged in via ethernet and serving as my WiFi router, connected to an ADSL modem. I've never unplugged the Time Capsule from the iMac. Time Machine has worked without complaint since I got the machine in December.

    I told Time Machine to not backup, in the hope that it would magically work at the next scheduled backup.

    And then rather than wait, I decided a few minutes later to manually start a backup. When I did this, Time Machine apparently found the Time Capsule backups and did an incremental backup in the same save-set. So it's all good for now, but I'm a bit puzzled as to what happened.

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