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Time Machine Back Up - I only get about 3 weeks.

483 Views 4 Replies Latest reply: Mar 25, 2013 4:59 PM by Linc Davis RSS
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Mar 25, 2013 1:52 PM

Time Machine Back Up - I only get about 3 weeks.


Is there a setting to tell it to go farther back or is it a space issue on my external hard drive? 


If so what external hard drives / sizes are recommended?  I'd like to go back a few months or longer.

Mac OS X (10.5.4)
  • drdocument Level 4 Level 4 (2,995 points)

    See here.

    And here.

  • Kappy Level 10 Level 10 (221,005 points)

    A Time Machine backup drive needs to be at least two or three times the capacity of the drive backed up. For example, if your computer's hard drive is 250 GBs, then a Time Machine backup drive needs to be between 500 and 750 GBs. The larger the backup drive the less frequently you will fill up the drive and see:


    About TM "Backup Drive is Full"


    Alert TM only deletes older files if they have been deleted from the source and when TM needs space on the backup drive for a new incremental backup. Time Machine "thins" it's backups; hourly backups over 24 hours old, except the first of the day; those "daily" backups over 30 days old, except the first of the week. The weeklies are kept as long as there's room.


    So, how long a backup file remains depends on how long it was on your Mac before being deleted, assuming you do at least one backup per day. If it was there for at least 24 hours, it will be kept for at least a month. If it was there for at least a week, it will be kept as long as there's room.


    Note, that on a Time Capsule the sparsebundle grows in size as needed, but doesn't shrink. Thus, from the user's view of the TC it appears that no space has been freed, although there may be space in the sparsebundle.


    Once TM has found it cannot free up enough space for a new backup it reports the disk is full. You can either erase the backup drive and start your backups anew or replace the drive with a larger drive.

  • drdocument Level 4 Level 4 (2,995 points)

    One thing that's helpful to remember is that TM keeps a copy of every different version of a file, so large files which are frequently modified can take up a lot of space in a TM backup.


    My strategy is to move files which are no longer needed (like finished projects), files needed only for reference (manuals), software installers, and the like, to a separate Archive drive which is automatically cloned as a backup, and use Time Machine only as a backup to restore part or all of my startup drive.


    In this configuration I have a 500GB Time Capsule for Time Machine, which keeps more than a year of backups of the 250GB or so of data on my startup drive. That is the low end of the recommended size for a TM drive (2x amount to be backed up), but in my view there is no sense using up TM space for "archive" type files which are for reference only.

  • Linc Davis Level 10 Level 10 (107,555 points)

    Do you use virtualization software, such as VMware, Parallels, or VirtualBox?


    The virtualization software creates a large virtual-disk container that is constantly changing, so it has to be backed up every time Time Machine runs. That will quickly fill up any backup destination.


    You should exclude the virtual-disk file(s) from your Time Machine backups. To do that, click the Options button in the Time Machine preference pane. Back up the files on the virtual disk from within the guest system, using a native backup application.


    A compromise solution is to create a "snapshot" of the virtual machine in the virtualization software (not a Time Machine snapshot.) That will give you a single large file that never changes and only has to be backed up once. All the subsequent changes will be stored in a new file that's initially much smaller, but will grow over time. You should still exclude that file from TM backup. If you ever need to restore the VM from Time Machine, you'll have a working setup, which will make it easy for you to restore the rest of the data from within the guest system.


    Another common cause of large TM snapshots is native OS X disk images. If you store a lot of data on one or more writable disk images, they should be in "sparsebundle" format, which will be backed up much more efficiently than any other format. Also be aware that disk image files are not backed up at all while the image is mounted. Make sure you unmount the image often so it can be backed up. If you ever restore, you will, of course, lose all changes made since the last backup. Consider eliminating large read/write disk images from your workflow, if possible.


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