I belong to a local computer club in my area and in response to some of our members' interest in equipping their desktop PCs with removable HDD/SSDs I prepared the following which may be of some interest to you.
Assuming you have one or more vacant available 5 1/4" external bays in your desktop PC case, you may want to give serious consideration toward installing a mobile rack/removable HDD/SSD in one or more bays. The advantages of doing so are enormous as I believe will be explained in the following document.
The mobile rack model we use virtually exclusively on the desktop PCs we build is the Athena Power MR-125PB
http://www.newegg.com/Product/Product.aspx?Item=N82E16817995104
This mobile rack is a two-piece affair - a removable tray and the rack itself which is affixed to the desktop PC's 5 1/4" bay (identical to affixing an optical drive or some such 5 1/4" device). This model contains a small fan that is dead silent in operation. The rack is dead-flush with the case's front bezel.
Installation of the rack is a simple affair; no more difficult than installing an optical drive.
What we particularly like about this Athena mobile rack model is that it's equipped with an ON-OFF power switch button, a most desirable feature in our opinion. Assuming a user is working with multiple removable hard drives in their mobile racks or has also installed a fixed internally-connected hard drive, it's a simple matter to press the ON-OFF button and "on-the-fly" temporarily disable one or more of the mobile rack's hard drives without the need of using the rack's lever to remove the rack's tray (caddy) containing the HDD or SSD from the rack's internal SATA power/data connectors.
Of course should the user choose to do so it's a relatively simple matter to press the removable tray's lever release button and thus physically disconnect the removable tray containing the drive, thus disconnecting the rack's HDD/SSD SATA data/power connectors from the mobile rack's connectors. A simple pull of the tray's lever is all that is necessary.
And should a user desire to employ additional HDD/SSDs for one reason or another, he or she can simply remove the present disk from the tray and plop a different one in. Thus, users have an UNLIMITED number of drives at their disposal with this device. A simple no-nonsense procedure that's accomplished from their computer chair. So the user can easily work with multiple OSs on different drives and access each at the simple press of the rack's power button. And comprehensive backups of one's system can be achieved just as easily.
So with a removable HDD/SSD, one gets the speed advantages of an internally-connected drive (not a USB external drive) and the absolute security of the backup/storage data on that disk by easily disconnecting/uninstalling the disk from the system whenever it's needed. Again, all from the comfort of his/her computer chair.
The one negative to this particular mobile rack is that it's designed to house 3.5" drives and not 2.5" drives (SSD), however, for the past few years we've been installing SSDs in the rack without any significant problems. In the past we simply cut up a couple of foam pieces (the type of stuff you frequently get as packaging material) and butt the pieces against the 2.5" drive so that it's firmly situated in the rack. Seems to work fine.
Another alternative is to drill two small holes in the bottom of the rack so that they're oriented with the screw holes found on the bottom of the 2 1/2" disk. Then screw the drive to the rack. Works quite well as long as you can properly orient the drilled holes with the screw holes of the drive.
And I'm aware of other users who simply use packaging tape for this purpose.
Lately we've found that by using adhesive strips (Scotch brand & others) to the bottom of the SSD (or to the tray itself) works just fine. And it has the added advantage of easily removing the SSD from the tray and inserting another SSD when the need arises.
Over the years we've probably installed a few hundred of these racks in the desktop PCs we've built and for other users. We've encountered very few problems with these racks and found no negative implications involving performance & longevity aspects between drives installed as removable drives and drives directly connected to the motherboard's SATA data & power connectors. While this particular rack & removable tray are fashioned from hard plastic they've held up quite well over the years. We've have encountered very few defective racks/trays and they're used quite extensively in our operations.
I can virtually assure you that once you begin working with one or more of these mobile racks that contain removable HDDs or SSDs you'll never want to build another desktop PC that's not equipped with one or more of these mobile racks. They're that good.