I am thinking of buying a 2 TB WD My Passport Ultra External Hard drive and I'll be using it with both OS X and Windows. I am planning to use this drive for my Time Machine data backup after creating additional partitions in the external HD. I will also be storing a large number of files of Music, Videos, VMs(>4GB) and software setups.

I know the limitations of Fat32 that it can't be used to copy files that are greater than 4 GB and of exFAT that it is prone to data corruption and chkdsk errors. I am confused on how many partitions should I make and what should be the formatting scheme on each partition? Also I want to know how much space should I leave on external HD for Time Machine Backup? I'll be backing up data only after a month or two, and my MacBook Pro has 256 GB SSD out of which around 220 GB is in use.

1 Answer 1


According to this article you can get OS X to read and write to NTFS, so if you are planning on using the disk for both, then go with NTFS. The one thing you need to check is if Time Machine will write to NTFS. It writes to NAS's which are not using an Apple proprietary file system, so it may work okay, just check before you commit to it.

As for partitions, the way Time Machine works is that it lays down an initial backup and then does incremental backups so that you can do things like go back in history and recover an accidentally deleted file as well as restore a Mac completely. It gives you each backup point in the most recent month, then it makes one month archives back for as much space as you give it. It starts to delete old archives when it runs out of space. You could probably get by with a 500GB partition for you 250GB SSD. You may want to consider 750GB if the go back to previous versions option sounds important to you. If not, go with the smaller partition and then you can have more room on the other partition for media archiving.

I am going to add a word of caution. In my personal experience, external USB HDD's are extremely unreliable. Almost every one that I have purchased, especially Western Digital Passports have bricked on me. I have lost data as I was doing the same thing you were doing and was extending my storage. I learned better.

Your best bet if you have a router is to get a two disk NAS that you can set up via ethernet. Internal Drives, especially HGST tend to be far more reliable than their external cousins. Two disk NAS from Synology is reasonably priced, easy to set up, and will give you the added benefit of being able to set it up as a RAID, which provides an added level of protection in that if one drive goes bad, you can always swap in a new drive and have the RAID rebuilt. RAIDs are not fool-proof, so you want to make sure you have a back up of this as well. Here you can take a gamble with an external USB HDD as your data is on the more reliable NAS.

  • I've been through probably 50 hard drives, any that were thrown out were due to the size itself no longer having value. But I've also lost a half dozen external drives due to failure. +1 for your advice. Jul 26, 2015 at 14:03
  • @AMR: Thanks for your advice. The real reason for getting an external HDD is because of the limited 256GB SSD that I have on my Macbook. I don't use HDDs for data backups, but since I'm getting this HDD so I thought why not also backup my data using Time Machine. All of my sensitive data is already backed up on Google Drive. But I still hope that my external HDD serves its purpose for at least 3 years if not more.
    – Aneef
    Jul 26, 2015 at 14:27
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    @Aneef. What I have done to extend the capacity on my MBP is use SanDisk Cruzer Fits The are very reliable and much faster than even a 7200RPM External Hard Drive. Plus they go with me and because of they do not extend more than a few centimeters, I am not concerned about them snapping. I don't use them for Time Machine, just for extended capacity for data files. If you get a USB hub, then you can get a lot of storage.
    – AMR
    Jul 26, 2015 at 15:08
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    I have a Synology NAS and that has been very reliable. The center drive of a 5 disk array has gone bad twice, but the other for are the ones I bought when I set up the device. I suspect that the center disk gets hotter than the others and that was why both fails happened in that bay, but all I had to do was get a new drive, pull out the old one and plug in the new one and the RAID rebuilt itself. I realize I have had some bad luck, but I have never had an external HDD that I used regularly that has lasted three years.
    – AMR
    Jul 26, 2015 at 15:13

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