Partitioning large hard drive for time machine and Windows

macOS & Mac Apps

Hi all
I'm about to get my first Mac, I baught a 21.5" iMac 2.9 GHz. I also want to run Windows on it, but don't want to install Windows on the internal 1 TB hard drive, I'm going to install it on a external drive and just boot from the external drive whenever I want to use windows. Now my questions:
Option 1
I have a 2 TB Seagate external HDD, if I partition it in to 2 seprit spaces say 50/50, would I be able to install Windows on the one partition and use the other partition for Timemachine backup? Then I have my other 1 TB external for general mass storage. Will this work, will the Mac be happy with this? I'll obviously give each partition the correct file format.
Alternitivly I can dedicate my other 1 TB external for Timemachine backups and then partition the 2 TB external for 1 part Windows and other part just some mass storage.
Option 3, I can also dedicate the 1 TB external for Windows and then partition the 2 TB external for time machine and general mass storage.

Guess the main question remains whether the Mac will be happy with a external hard drive partitioned in to different file formats, just on a side note my 2 TB is a USB 3 Seagate and my 1 TB is a USB 2 Seagate.

Thank you



Submitted by Chelsea on Sunday, August 31, 2014


I don't know much about time machine, as I don't use it. However, I can speak to running Windows and partitioning drives on OS X.

The actual partitioning of the drive can easily be accomplished with disk utility. I say easily because I could never do anything like that on a windows system. One thing that people get tripped up on: there are text boxes once you create the partition to size it where you can just type in the size and not have to fiddle with the sliders.

Now to the "Which drive should I use?" question: Remember that, in general, throughput is determined by two things: the speed of your drive and the speed of the interface it is attached to. so your external drives might be faster (higher rpm) than your internal one, but because USB might not be as fast as your Mac's SATA? interface, it will feel slower. I have no experience with USB 3, but would not recommend USB 2 for heavy operating system use unless you want a real lag of about a second between key presses. But that's just me.

Now for the size: I've heard time machine can be a real drive hog, so partitioning for that is a great idea. Unless you have lots and lots of stuff, though, you shouldn't need a whole terabyte for Windows. I can run both Os-Es fine on my 128 GB SSD. Also, if you want to virtualize rather than going with a dual-boot, you can just move the VM around and it will grow as you add more things to it. Also be aware that if your hard drive starts dying, things on both logical disks might be affected since you only have one physical disk.

Hope this Helps and sorry for repeating stuff you might have already known about,

Submitted by synthesizer101 on Sunday, August 31, 2014

I haven't had any problems booting from a partition on an external drive. I can't say I've run windows this way, but I have run other mac OSX and Linux from part of my external. It worked well. However, I really think using the USB3 drive for anything that will be booted is a good idea. USB2 for mass storage is fine, but the extra speed will be much better placed with the actual OS.

Submitted by J.P. on Sunday, August 31, 2014

While I do not understand your reasoning to proceed this route. Which might be right for your specific situation. Have you considered a less involved and time consuming option like running VMWare?

Submitted by Nickus on Monday, September 1, 2014

Hi all thanks for the replys.
Firstly, I don't want to put Windows on the internal 1 TB drive because it will eat up a lot of space, I have a lot of things which I want to put on there, just my iTunes library alone is already almost 200 GB.
I read elseware that USB 2 is not recommended for a drive which you want to boot from, so then using my 1 TB external for Windows is out of the question, luckally my 2 TB external is 7200 RPM and USB 3.
Now you mention VMWare, I herd in the past that it's quite slow compared to installing Windows directly via Bootcamp, is this true or is it fast enough and useable if you run it as a VM?

Chelsea, you mention I can move the VM around as it grows, does this mean I will be able to move the VM folder around between the internal drive and externals, maybe keeping it on the 2 TB external in the end? Will it be as simple as cutting and pasting the VM folder to a different location, will it still work after I moved it to a different drive?

Submitted by J.P. on Monday, September 1, 2014

I personally don't have issues with VMWare. Not to mention it doesn't eat up hard drive, internal or external. If you decide this route, Fusion is way more accessible than Parallel. Once you figure out keyboard and shortcuts, quite easy to use.