reformatting external HDD & Time Machine

Discussion in 'Mac Basics and Help' started by Flake, Mar 5, 2011.

  1. Flake macrumors regular

    Flake

    Joined:
    Apr 18, 2010
    #1
    I have a 500gb external hard drive that I'm thinking of using for Time Machine backups. It's about half full now and formatted in NTFS, and as I understand it Time Machine will only work will the Mac OS Journaled format? (even if I installed the NTFS 3G thing which will allow writing to NTFS?) Is there any way I can reformat a partition of the external drive without deleting any content on it to use for Time Machine?

    Also how much space do Time Machine backups take up? I have a 128gb Macbook Air if that helps.
     
  2. Makosuke macrumors 603

    Joined:
    Aug 15, 2001
    Location:
    The Cool Part of CA, USA
    #2
    To start with, Time Machine backups take up as much space as they need to, limited by time and how much data is on the drive.

    At minimum, they'll take as much as the amount of data you have stored, plus a little. Past that, they will continue expanding to keep a copy of all changed files in increments of hourly backups for the last 24 hours, daily backups for the past month, and weekly backups for everything older than a month. If the Time Machine partition runs out of space, it will start automatically deleting the oldest backups as necessary.

    It's pretty efficient, but how much space it will take up depends entirely on how you use the computer--if you only do web surfing, email, and text documents, the rate of increase will be very small. If you're constantly editing video or adding and modifying large photos, it could bloat quite quickly.

    My personal rule of thumb is to leave about the same amount of space as the drive I'm backing up, but that only works because I try to keep the boot drive no more than half full, and I store most of my large media on a separate drive backed up with a different tool.


    As for your main question: No to both. As you gathered, Time Machine won't officially back up to a directly connected NTFS volume--it requires HFS+. You CAN do some unsupported modifications to allow it to back up to other filesystems, NTFS included, but it's a bad idea in my opinion--I've heard of occasional issues while writing to NTFS volumes via the 3rd party tools, I've had problems myself once or twice, NTFS access tends to be slow with the drivers I've used (which would be annoying given that TM runes every hour and can do a lot of drive access), and even if it worked smoothly you're sort of asking for trouble with your backups using an unsupported configuration. And of course the moment it decides to go haywire will be the moment you actually need something.

    Changing the format of an NTFS drive to HFS+ without erasing it also not possible, and again, even if it was, if you don't have a backup of the stuff on the NTFS drive you're asking for trouble if something goes wrong with the process. And if you do, you can just reformat and copy over from the backup. Note, also, that Time Machine is going to work best with its own partition to write to, so I'm guessing here that you'd be splitting your external into, say, a 300GB data partition and a 200GB TM partition, or something similar. Which will work, again with the limitation that the data partition has no backup.

    If the data on your external is at all important, I'd just spend the extra hundred bucks for a second external of at least 750GB (I'm assuming here these are 2.5"; if you don't mind a 3.5" you can get 2TB for around $100), then divide it into data backup and Time Machine partitions. You might also use the opportunity to reformat your external to HFS, if you don' t intend to use it on a Windows machine anymore.
     
  3. Flake thread starter macrumors regular

    Flake

    Joined:
    Apr 18, 2010
    #3
    thanks a lot for your help :)

    so just to confirm, I don't need to reformat the entire drive to HFS+, just a partition? (I can move everything I already have on it and then move it back so having everything erased won't be a huge issue)
    one more thing, what if I don't connect the drive to my computer for a few days or weeks?
     
  4. Makosuke macrumors 603

    Joined:
    Aug 15, 2001
    Location:
    The Cool Part of CA, USA
    #4
    Yes, Time Machine is perfectly happy running on just a partition. Assuming you're only intending to use the drive with a Mac, you should probably format your data partition as MacOS Extended (Journaled) as well, as it'll be significantly faster, and probably more stable. In which case you'll also want to make make sure you change the partition map scheme from MBR to GUID while you're at it. It's possible, I assume, to have an HFS partition on an MBR drive, but also probably isn't the best idea, and there's no benefit to it.

    If you don't have your Time Machine volume connected for a while, it'll just start initiating backups once it does become available. Alternately, if you set up a Time Machine drive, but then turn Time Machine off, you can select "Back Up Now" from the Time Machine menu item any time you want to do a manual backup. This is what I do with my laptop; less secure (in that if I forget, no backups), but it saves the network access when I'd rather keep it fast (I run my backups to a network server).
     

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