I just recently acquired a Mac Mini Mid 2011 model. This model does not come with an optical drive, and has space and the correct hardware to add an additional hard drive. iFixit sells a kit that contains everything you need to take your Mac Mini and add a second hard drive yourself. The kit is so popular that I have been on the waiting list to buy one for almost two months now. It’s a great kit, the instructions to disassemble and install the new hardware are very thorough. I couldn’t be more pleased with iFixit’s offering.
Now this particular Mini is used to run all of my virtual machines and also used as a file server. As such, I want the machine to have as much storage capacity as possible while providing snappy IO for my virtual machines. In order to maximize storage, I do not want to use an SSD drive. So, I wanted to use two 7200RPM drives with a large drive cache, and as much storage capacity as possible. I popped over to NewEgg.com and searched for 7200 RPM drives in the 2.5″ form factor and found the Seagate Constellation at 1TB. Perfect! Plenty of capacity and pretty high speed. Well, after reading the product details, it turns out the drive is 15mm thick! I didn’t think it would likely fit, but I thought I might as well ask on iFixIt and see if anyone had tried this. So I went to the “Ask a Question” section of iFixit. After reading the instructions, it said that only repair questions could be asked in that forum. Well, I am not doing a repair, I am upgrading. So I followed the instructions and asked in the “iFixit Meta” section instead. The question was whether anyone knew if two 15mm drives would fit inside of the Mac Mini with the dual hard drive kit. The question was deleted within 12 hours without any feedback from iFixIt. They didn’t tell me it was in the wrong section, or anything. It just up and vanished. Two days later, I get an email from iFixIt indicating that two people had responded to my question and that they wanted me to select the answer that I felt best answered the question. The responses are below:
As far as i know two drives 9.5 mm is your current option, and a “fast” 1TB drive in that size isn’t around yet as far as i know.
Western Digital makes a 1TB blue line that should work fine.
You would have to go a bit smaller 500-750GB WD’s black line for a proper fit and a higher performance drive, Black line also has advanced format models, 4k sectors, allowing for more useable space after formatting then a regular drive……..and a 5yr warranty……..Black line drives are quick …….some people have claimed to get a 12.5 to work with some “modification” however you risk damaging the computer.
Hatachi [sic] makes some nice drives too…….. i am most familiar with WD’s line as i have been using them for years.
hope this helps.
And then:
The answer is ”’no”’. Please see step 7 [guide|6131|here]. There is only 15mm of “extra space” underneath the factory original 9.5mm drive. Actually for a number of reasons should not attempt to put 1 in there with a standard 9.5mm drive. Read the reviews on the Seagate Constellation.2 ST91000640NS hard drive. It is a power hog the Mini’s power supply more than likely couldn’t power it up and if it did you would suffer other consequences in the USB realm and others. It runs very hot, not a good thing in the mini. If you got to have internal Terra [sic] drives go with the newer WD Scorpio Blue Or the Samsung for inside the Mini.
Personally with a Mini. I would go with a SSD for my operating system, virtual memory and programs.Then a larger slower hard drive for data. It is actually the hard drive that the virtual memory is placed on that makes the biggest difference in a computers performance. After that, it is the hard drive the operating system is on that determines how snappy a computer performs. Your data hard drive doesn’t need to be fast. It needs to be reliable.
I wish that I had the opportunity to thank them for their answers, but I was not given the chance. It was helpful to learn that the mini only has room for 9.5mm drives. This means even the original Western Digital Scorpio Blue won’t fit, since they it is 12.5mm. In fact, only two 1TB drives will fit, as far as I can tell. Those are the Samsung Spinpoint M8 and the newer Western Digital Scorpio Blue.
In fact, the first responder was much more helpful than the second, who seems to like to make things up. For example, the Constellation maxes out at about 5.96W of power consumption. It idles at under 3W. This is not much different than a standard hard drive. As you can see here, even SSDs can consume around 3W of power. And then to suggest that the hard drive’s power consumption could cause problem for USB devices? Perhaps if the hard drive put the power supply at 100% capacity. But if Apple had put the Mac Mini at the limits of it’s power supply’s capacity, then the unit would run very hot and not be very energy efficient. Typically you would never design a unit to run above 80% power consumption. The Mac Mini idles at 10W and maxes at 85W (Apple). I can’t find specs on the actual power supply but I would expect it to be at least 110W. If it is 110W, then a maxed out Mini is only using 72% of the power supply’s capacity. So therefore, the hard drive’s power draw should be insignificant.
I also have this box maxed out with RAM, so hopefully it is never using virtual memory, and his “put the virtual memory on the SSD” comment is a moot comment. Regardless, I already stated that I wanted to maximize storage capacity + speed, and therefore his SSD comment is pointless in any regard.
As for his statement “Your data drive does not need to be fast…”, well I disagree with that, obviously. Otherwise, I wouldn’t want to have fast data drives. Let me tell you why. First of all, I run many virtual machines and they will not all fit onto any economical SSD. I want them to be as responsive as possible because they provide services such as: VPN, calDav, CardDav, email, and remote desktop service. I run a Windows XP image that I can remote into from work, my phone, or my tablet. This XP VM has to be fast to save time and battery on my mobile devices. In addition to all of that, I stream media to and from the machine as my HTPC copies recorded shows to the Mini for processing. So maybe he doesn’t need fast data, but other people do. Otherwise, they wouldn’t make fast drives in that capacity. 
In any event, thank you to the first responder, who did provide me with valuable insight. Also big thanks to iFixIt, for deleting my question without even telling me why! I am just thankful their system is so broken that it emailed me the responses to the deleted question anyway.