External drive encryption

With my bride’s and my new M1 laptops…I’ve naturally got FileVault enabled and I have both a spinning drive formatted HFS+ with CCC clone and TM partitions for each laptop as well as a couple of Samsung T7 SSDs for backup and photo storage on travel…the latter are APFS drives with 3 plumes each, one for a clone of each laptop and one for cloning just the images folder on my laptop as we will only carry a single laptop non travel and brides photos go into Lightroom on mine anyway…no TM plumes on the SSDs since TM requires HFS+.

Is there a good reason not to just encrypt the SSDs and spinning drive and store the passwords in the keychain? The drives might get plugged into our iMac occasionally but I can just type the password there or store it in that keychain as well. I’ve never encrypted external backup drives before but considering these will be carried on travel it seems like a better idea to do so for these.


A few comments:

  • Plumes? I’ve never heard that term to refer to disk partitions/volumes.

  • Why not use APFS for the CCC clone? It works on a spinning hard drive, and use of snapshots is really convenient for tracking files from older backups. (Much more convenient than digging through the SafetyNet folder CCC uses on HFS+ volumes)

  • Starting with Big Sur, Time Machine can back up to an APFS volume. It should work more efficiently, since it will use snapshots instead of massive sets of hard-links to manage all the historic backups. It is Apple’s preferred TM mechanism, if your’re running Big Sur or later. Howard Oakley seems to prefer it as well.

    Unfortunately, you can’t convert a Time Machine volume from HFS+ to APFS. If you want to switch, you need to completely erase the device, losing your backup history.

  • No technical reason why you can’t encrypt the external drives. The encryption is hardware-accelerated (as should be the case on any M1 Mac or Intel Mac with a T2 chip), so you shouldn’t see a performance problem.

    I would choose to not store the passwords in the keychain. This way, if your drives are stolen with the computer, it will be that much harder for the thief to get your data. Although I suppose it’s moot, because he’ll have access to the original data if he can log in to the laptop. I guess it depends on how paranoid you feel.

    When I travel, I transport a few sensitive documents (budget spreadsheets, checkbook, etc.) with me. Since they’re small, I place them in an encrypted disk image on the computer I travel with. I deliberately do not store the password in the keychain, for the reason I described above. Fortunately, I’ve never had to test this theory.


David…thanks for the comments…

Volumes…not plumes, darned autocorrect got me.

I considered APFS for the spinning drive…but it’s designed for SSDs and according to google search is slower than HFS+ for spinners…and TM requires the latter (didn’t realize that was no longer true).

I hadn’t realized that TM now would use APFS…now that I see it can be I will probably reformat the spinner.

I thought about not putting the passwords in the keychain…but they would be useless unless the thief cracked the machine password…and I’m probably not paranoid enough to not store them…although I might on my wife’s laptop since it won’t be traveling with us. Alternatively I can use a long but memorable password so my bride doesn’t really have to remember it or open her password manager to get it.

Thanks for the comments…things to consider for me.

These days there’s really no more good reason against using APFS on spinning drives for TM. The advice is to perhaps avoid APFS on HDDs if they’re going to see loots of read/writes like on a boot volume (my advice would be to simply no longer boot any Mac routinely from a HDD at all, it’s just too slow and leads to poor user experience). But if it’s TM or some more long-term storage, APFS is the way to go.

Here’s Howard Oakley’s recent take on it.


IMO, APFS is definitely slower than HFS+ on rotational media. But depending on your use case, the added features are worth it.

I like to use it for backup/clone volumes because snapshots are the most convenient way of managing historical backups. And (at least on an Intel Mac), you can still make a bootable clone (but who knows how much longer we’ll be able to do that).

For a working volume (e.g. temporary files, caches, live databases, documents for apps that don’t load them completely into memory, etc.), I would stick with HFS+. For these situations, the performance benefits outweigh the benefits of APFS features (snapshots, fast file duplication, etc.)

Of course, many people will question the need to use HDDs at all. That (IMO) is a matter of personal preference.

For backups, I think the ability to have massive capacities is most important. Each of my backup volumes is 4TB, backing up a 2TB internal SSD which is currently 50% full. This gives me room for a lot of snapshots before old backups will get purged.

For working storage, I think it all depends on where on the price/performance curve your preferences lie. I’d recommend an SSD, but I wouldn’t criticize someone who is unwilling/unable to spend the money needed to get a good quality high capacity SSD.

Thanks Simon…I was poking around his site again earlier and ran across that post. So I’ll just reformat the spinning drive before creating the volumes. Besides the snapshot ability…there’s the 'you don’t have to assign a fixed size to a volume’ which shares space better and can assign reserved as well as maximum spaced so it’s a more flexible drive space usage plan.

It’s still cheaper for HDDs if you want large sizes…a 4 TB OWC one is $200 and a 4 TB SSC in the same case is $950…so cost per GB is a lot less with an HDD as long as you don’t really need the speed. I’m using both the OWC HDD and a pair of 2TB Samsung T7 SSDs to backup both my M1 Pro MBP and my wife’s M1 MBA but will carry only the Samsungs on travel for weight and size. For the one that likes in the end table drawer and gets hooked up periodically for backups the cheaper option is fine.

Sounds like a solid plan. There’s clearly still a significant cost advantage for HDDs over SSDs so if you’re primarily interested in backing up large amounts of data, it sounds like formatting a many-TB HDD as APFS is a cost-effective and good solution that won’t break the bank.