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I just got a 2TB external hard drive, and I want to use it to backup my 3 Windows computers and my MacBook Pro. If possible, I would like to create 4 subdirectories on the external drive - one subdirectory for each computer. Can I tell Time Machine to put my MacBook Pro backups into one subdirectory, so that it doesn't affect any of the other stuff on the external drive?

BTW, I will be installing one of those NTFS drivers for the Mac OS X, so that it can write files to the NTFS-formatted external drive.

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Is this a Network Drive or an USB drive? If USB, do you want to replug it every time? Additionally TM doesn't work with NTFS so you would need two partitions anyway, one with HFS+ and one with NTFS. –  patrix Dec 21 '12 at 19:34
    
What partition type did you use for the 1 TB drive in this case? GPT? Time Machine requires a GUID partition type, correct? So are GUID partition types used for the entire disk and work fine for the NTFS backups? –  user49281 May 13 '13 at 15:55
    
I used the Master Boot Record because Windows 2000/XP do not support the GUID Partition Table. Master Boot Record works fine with Time Machine. –  pacoverflow May 16 '13 at 7:34
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up vote 3 down vote accepted

Your preferred setup is not possible: OS X can't share an NTFS disk with Windows for backup because Time Machine needs HFS+ (from http://support.apple.com/kb/HT1427):

Manually preparing a new disk for Time Machine

(...)

If you want to partition the disk, click the Partition tab and select a layout. Make sure "Mac OS Extended (Journaled)" is selected in the Format menu for the partition that will be used for backups. Click Apply.

Luckily, you don't need two separate drives. Using partitioning you can trick your computer into thinking it is connected to more than one drive, although there's only one. In this case, two partitions will suffice, one HFS+ and one NTFS.

(Why only one NTFS partition although you back up 3 Windows computers? Because Windows stores backups in folders named after the computer name so there are no conflicts whatsoever (see this post). You can use one NTFS partition to store backups of multiple Windows computers.)

I'd recommend that you create the HFS+ partition on your Mac first, then, on your Windows computer, format the other partition to NTFS:

  1. Plug your drive into your Mac.
  2. Open Disk Utility (in Applications/Utilities).
  3. Select the drive and select the Partition tab.
  4. Create two partitions. Format the first partition as HFS+ (and give it a name like "Time Machine"). Leave the other partition as "Free Space". See here for more details.
  5. Eject the drive and plug it into your Windows computer.
  6. Format the second partition as NTFS.

When you're done, plug the drive again into every Mac/Windows computer and select the corresponding partition as backup drive (see here for OS X and here for Windows).

To prevent the NTFS partition from being mounted every time you connect the drive into your Mac add this entry to /etc/fstab (as explained here):

LABEL=BACKUP_WINDOWS none fusefs_txantfs noauto 

Replace BACKUP_WINDOWS with the NTFS partition name.

This setup works like a charm.

I have a very similar configuration:

My external 1 TB drive, which I use for backing up my Mac and my wife's Windows PC, has two partitions called "Time Machine" and "BACKUP_WINDOWS":

enter image description here

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Thanks for the great answer. Is there any problem with letting Mac OS X mount the NTFS partition every time I connect the drive? –  pacoverflow Dec 23 '12 at 1:15
    
I'm glad I could help. About OS X mounting the NTFS partition: I used to mount both, but once I had a problem. I ejected both partitions after backing up my Mac and later, when I plugged the drive into my wife's PC, Windows complained the drive had been unproperly disconnected. So I decided not to mount the NTFS partition on OS X. –  jaume Dec 23 '12 at 13:37
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Thanks for your detailed explanation. I wanted to buy a new external hard drive for my mac backup. but now I will share my external drive for win and mac. by the way, I used the following in my fstab file:

LABEL=BACKUP_WINDOWS none ntfs noauto

I replaced fusefs_txantfs with ntfs, since that did not worked for my OS 10.9.1

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