12 Replies Latest reply: May 7, 2012 7:41 AM by etresoft
bettyfromst. george Level 1 (0 points)

I'm going to apologize upfront if the answer to my question seems obvious, but Mac OS and Time Machine is all new to me.


There is a possibility that there is something amiss with my external hard drive.  I have ejected the hard drive and read in a thread that there is a way to disable TM's continuous "local Snapshots" Backup with a command typed in Terminal.  The reasoning is that TM uses a lot of CPU's? and things can become a bit sluggish.


Anyway, here's my question:  If I turn TM to "OFF", doesn't this stop the hourly snapshots on the INTERNAL hard drive?



Mac OS X (10.7)
  • captfred Level 7 (26,290 points)

    Yes.  Just turn TM off.

  • Grant Bennet-Alder Level 9 (56,585 points)

    The reasoning is that TM uses a lot of CPU's? and things can become a bit sluggish.

    I am not sure where you got that from.


    My experience on a MacPro is that it uses less than two percent of the CPU, over about five to ten minutes an hour, to run the backup. It appears to be optimized for minimum disruption to your work, not for completing in the shortest time.

  • thomas_r. Level 7 (30,717 points)

    If you turn TM off, yes, it stops making those local snapshots.  But then you stop creating backups entirely, which is never a good idea.  Are you using some other backup software in addition to Time Machine?


    I use Time Machine, and keep the local snapshots feature turned on, and have never seen any sluggishness as a result.  Time Machine will not cause such a problem unless there's something else wrong.


    There is a possibility that there is something amiss with my external hard drive.


    This is very cryptic, as you provide no details, and don't link this statement in any way to the rest of your questions regarding Time Machine.  What symptoms are you seeing that lead you to believe there's something wrong with an external drive?  Is this drive used for Time Machine backups?

  • bettyfromst. george Level 1 (0 points)

    Yes, my LaCie was set up to be used for Time Machine backups.


    When I started to have problems with TM approximately 2 months ago, I had contacted Apple and they walked me thru repartitioning the external hard drive.  But I continued to have problems with TM saying "failed" cannot complete back up.


    I would eject the LaCie and upon reconnecting, it would then backup.  But it continues to periodically fail even after the repartitioning.


    I went to system.log via Console and looked at the backup logs and it said: "Back up Failed with Error: 2


    I sent this info. to Apple and specifically asked, what is this Error 2 ?  Thinking that this would give an explanation as to the failure.


    Apple never responded to my question.  They said that I should get another hard drive and test it.  There could be something wrong with my current hard drive.


    So, with the LaCie ejected, I thought I was suppose to turn Time Machine Off.

  • thomas_r. Level 7 (30,717 points)

    Error #2 is defined as:


    #define ENOENT 2 /* No such file or directory */


    What this means is that the error means that an attempt was made to access a file or folder that didn't exist, and the error was not handled.  Errors should always be handled in a more user-friendly way, so seeing an error like this generally means that it was unanticipated...  ie, something went wrong that the programmers did not think was likely enough to bother writing code to handle it.  Unfortunately, knowing this doesn't really get you closer to a solution.  If you erased and repartitioned the drive, though, and the error is still occuring, that means either something you have installed is damaging it repeatedly or there's a hardware issue.  I would recommend trying a different drive, different cable and different port on your computer (only realistically possible if you're using one of the USB ports).


    Regarding ejecting the drive, that is precisely when the local snapshots are important.  They were added to provide a modicum of protection for users of portables, when away from their backups.  And they have already saved my bacon once, so I strongly advise leaving them alone.

  • bettyfromst. george Level 1 (0 points)

    Thanks for finding a definition for Error 2.


    I just tried a different port with the same LaCie to see what happens.  And turned Time Machine ON.


    One more question, with Time Machine ON and if I need to eject the external hard drive, does TM's snapshots include iPhoto?  My iPhoto library is starting to become large.


    Thanks for your help and advice.




    Also, since I had turned Time Machine OFF, does this mean that  all past snapshots were deleted?

  • thomas_r. Level 7 (30,717 points)

    The snapshots only contain one week's worth of files, and only files that have changed.  They won't contain your whole iPhoto library, just changes you make to it, and only within the last week.  So you've got to make sure you've got a working Time Machine backup on another drive, and that you're connecting it for a backup at least once per week, otherwise there can be gaps in your backup.

  • bettyfromst. george Level 1 (0 points)

    Thanks again for your help.


    Much appreciated.



  • thomas_r. Level 7 (30,717 points)

    No problem, glad I could help.

  • etresoft Level 7 (27,801 points)

    There seems to be some misinformation here. I can't entirely correct it because I don't have all the information.


    First and foremost, how big is your startup drive? How big is your time machine drive? How much space is free on each?


    Without knowing those exact values, it is hard to say anything for sure.


    I can definitely tell you that if you are noticing any problem with Time Machine, then Time Machine is not the problem. The last thing you want to do is turn it off. Find out what the problem is first. Time Machine runs in the background. If your machine is healthy and you are using a locally connected external drive, you should never notice Time Machine is running.


    How old is your computer? How old is the internal hard drive in it? Your internal drive may be beginning to fail.


    For the record, that error code is entirely meaningless. There are many such messages printed in system logs. They aren't meant for end users to dechipher.


    Local backups are simply Time Machine running without using the external hard drive. If you have a notebook machine, Time Machine always runs, even if your backup drive is not connected. It is not correct to say that the local snapshots only contain a week's worth of files. They contain all changes but are coalesced daily and weekly, just like regular Time Machine backups. When you connect your external drive, they are all moved to the main Time Machine disk. If you are noticing that the local backups are running, then something is seriously wrong. One possibility is that you are using Parallels/VMWare/VirtualBox or Entourage that is not optimized for how Time Machine runs. Parallels and similar programs have settings to allow you to exclude their data form Time Machine so you can back it up manually. If you aren't using these problems, and you are noticing local backups, then your internal hard drive is either full or about to fail. If the drive is close to 3 years old, either could easily be true.

  • thomas_r. Level 7 (30,717 points)

    It is not correct to say that the local snapshots only contain a week's worth of files.


    Pondini, our Time Machine expert, disagrees:




    regardless of space, Local Snapshots are periodically reduced to one per day after 24 hours, then deleted after a week.


    As to your claims that they get moved to the backup drive when you re-connect, that's a myth.  Connecting the backup drive has no effect on the local snapshots.  I actually tested that, back when I first discovered this feature.

  • etresoft Level 7 (27,801 points)

    I should not have gone into that level of detail about how Time Machine works. Time Machine is optimized for each system and can have different behaviour depending on a machine's configuration and operating system version. Apple can and does change Time Machine's behaviour on a regular basis.


    Some things, however, do not change. Time Machine needs to be at least twice as big as the hard drive it is backing up, preferably three times as large. Time Machine also needs free disk space on both the startup drive and the backup drive. Time Machine only backs up data. If your internal drive is failing, as they all do, it is importatnt to get it replaced. Sometimes, external drives can fail too.


    Normally, Time Machine does not cause any noticeable problems and should not fail on a regular basis. If it does, that means something is wrong and needs to be fixed. It can't be diagnosed by looking at low-level error codes. It can only be uncovered by asking the original poster about the system's free disk space and configuration.


    If turning Time Machine off significantly improves the performance of someone's machine, then something is seriously wrong.