If I connect an external, spinning drive to MacOS and encrypt it, are there risks to doing so?
Obviously the drive wouldn’t be readable by any computer that didn’t have the encryption key. I don’t really consider that a “risk.”
But let’s say the drive starts failing, read errors, etc. Is that any more of a risk to data recovery than a drive that’s not encrypted? Anything else I should be thinking about before I encrypt?
I’ve been doing this for years with my backup drives. Since I backup multiple computers (work laptops for my wife and myself, plus home iMac that contains all our personal stuff, financial info, and photos), I have usually had large spinning drives with multiple encrypted disk images that I use to clone those machines to (using SuperDuper).
I’ve never had an issue, although I do tend to replace the spinning drives every couple of years out of a sense of spinning disks being both fragile and not that expensive.
I just make sure that the encryption key is secure in Passwords (so the images can mount easily) and in 1Password (because belt and suspenders).
Hope this helps!
-Eric
How do you recover lost or damaged unencrypted files? IMO, the solution is the same. Good backups that are tested on a regular basis. The best backup would be unencrypted copies of the data. But that isn’t always practical.
I backup my encrypted external SSDs using Arqbackup locally and to Backblaze B2. And once a week to Time Machine. Then I restore a few files from each backup about once a month and make sure they are readable.
I learned the hard way. I started encrypting some files in the early ‘90s with PGP and only backed up the encrypted copies. Years later I couldn’t decrypt some of them because they had apparently become corrupted.
Simple answer: Depending on how the encryption is implemented, the effects of drive errors can be much more widespread when a drive in encrypted, up to the whole drive being unreadable.
(tl;dr: Yes)
Modified simple answer: The risk of untested backups leading to data loss is much, much higher than from encryption. Testing backups regularly as @WayneG suggests greatly reduces the risk of both.
Dodging the question simple answer: Risk based decisions are rarely simple 
This is a great idea. The physical disk itself is not encrypted and can be backed up or recovered using all the available tools including paid recovery services.
Then the full recovered encrypted disk image can be opened as long as you have saved and archived the encryption keys.
Basically, a layered approach much like networking and data comms where each layer has a function that doesn’t intermingle with the layers above or below except via well-defined interfaces.
Having said that, my personal use case doesn’t require encryption so I don’t have to deal with any of this.
Aren’t encrypted disk images even more likely to introduce problems, though? I seem to recall reading something from Eclectic Light that basically marvels at the fact they work at all, due to how Apple handles them.
I know that if you try to mount a 1 TB encrypted image it seems to take forever. I’m not quite sure why.
It can be slow to mount. But I haven’t had any problems yet (knock on wood).
-Eric
Interesting, worth investigating.
I think the OP was primarily concerned about disk media or physical disk drive failures.
While the potential for Apple’s disk image processing to be buggy or unreliable is certainly true, that’s a different dimension to the problem, I think?
Well, in this case I’m the OP, so I can clarify. 
I’m broadly concerned with risks/reliability of encryption when drive failures occur, and my impression is that creating encrypted disk images (as opposed to encrypting the whole drive) doesn’t decrease that risk. From what I’ve read, it might even introduce new risks. It definitely creates a performance drag.
I don’t want to swap types of risk. I want to minimize it overall.
I definitely get this, especially after having had Time Machine backups just fail completely on me on multiple iterations of my home iMac. (Three different iMacs, all of them have had Time Machine just stop working; and yet, it has never failed on any of my work MBPs.)
A risk factor that I consider, and that makes the “data loss due to encryption” risk worth it to me (and the equation will be different for everyone), is the risk of all my data that is normally safe in FV sitting there, in the clear, on an easy-to-walk-away external drive. Financial data, photos, and personal documents on my home machine plus information of varying levels of confidentiality on my work machine, make me want to have those backups encrypted.
I also have layers of backup, like a Backblaze account that is encrypted differently, so if that backup HDD or a disk image on it fails, I have another safety net.
-Eric
Maybe I’m being too pedantic, but is the issue failure or recovery of data?
e.g. If there is a failure of a drive or media, the risk profile is very different if the next step is to attempt some type of device or data recovery from the failed device, versus recovering data from backup or other copies.
Should also consider the time to recover. In addition to local backups, I have all my data backed up with Backblaze, but I don’t rely on it.
Backblaze recovery time could be days or a week if I am waiting for them to ship a drive to me, versus going online and downloading only a handful of files I deleted by accident.
(Online recovery of multiple GB or TB of data from Backblaze would also be time-consuming.)
The issue is failure, due to recovery time. Recovery of data is the ultimate goal, but I have a RAID 5 array with 20 TB, much of which is backed up to the cloud. If everything went kaboom, I have reasonable confidence I could get things back and working. But I don’t want any more “kaboom” than necessary. 
I always encrypt my external drives. The only hard job is to remember how I name them in the password manager.