Using a "stand" rather than an enclosure is appropriate if the disks that you buy are not hot running, they don't exceed 2TB, and you want to just buy raw drives, which are usually $10 or more cheaper, and if you are buying more than one. You avoid buying more boxes and just get minimal protection and size.
I call it a stand because the drive is upright in the base, connector down--2.5" and 3.5" SATA use the same connector. All drives, I know of, will run in any orientation but all do not like to be dropped or even shaken. When you get more than one be sure to label each one. You can shut off the power at the stand and should while changing them, perhaps. Just be sure the receiver has finished with it or if used on a computer that it has been ejected and any directories updated.
The good thing about the file system Dish uses is that it cares little about improper ejection but it is possible to mess up the internal references, if you try. The bad thing is that there are no common utilities for this FS, like for moving files or "garbage collecting."
As to use on a 211, I think this will do as well as any. An enclosure with fan might do better in a hot room or with neighboring electronics. I cannot tell you the best drive for heavy usage of delaying play and continual recording and playing. Hitachi makes good drives, there was a 2.5" in my MacBook as is the large replacement, but others make good ones also.
-Ken
Ken, thanks for the very informative answer. I expect that once a drive is installed on my 211k, that it will be either on or recording for a good part of the day, so I'll go ahead and get something like the Western Digital 1TB Elements USB 2.0 Desktop External Hard Drive, WDBAAU0010HBK-NESN.
Thanks