Time Machine excluding external hard drive

So I was helping a (novice) friend setup a new Ecotank printer to his M2 Mac Mini, and noticed he had two Western Digital USB drives connected to a Caldigit dock. One 4TB HDD had his archives, The other, an 8TB WD was empty. And no Time Machine backup. (for his credit, he was paying Apple for iCloud storage and setup his mac to have desktop/documents/etc in cloud).
After discussing his backup options, I was asked to setup the 8TB WD USB for Time Machine and noticed that the drive was EXFAT. I explained TM won’t use this unless APFS or Mac OS Extended (Journaled) so he was ok with me partitioning/erasing as APFS. Which once done, Time Machine prompt came up and asked if … yes, lets make it a TM drive.

In Time Machine Options, there is Excluded list and his archive HDD (USB) is there and unable to be removed from Excluded. Which means, it won’t be backed up (this is 500GB+ of archival work…it needs to be on Time Machine).

I ask: shouldn’t that HDD (another WD formatted as EXFAT) be repartitioned/erased as APFS or Mac OS Extended? (I can have that drive data backed off, then repart/erase, then restore it back). I know on my own mac, that my volumes are MacOS Extended (Journaled) can be excluded/included in my TM backup (I have some excluded for storage size issues).

(kinda answered this after I got home and looked at my external drives-they are APFS for CCC and MacOS Ext (Journaled) for TM to see and backup only select folders/exclude others).

It would be ideal for a popup that tells the uninformed External Drive user: Hey, you’ve connected an EXFAT drive. If your are using this with both Mac and Windows, there are some caveats. Thus, you cannot use for Time Machine, nor will Time Machine include files/drive for back ups. And other limitations like non-boot, repair tools, R/W access limitations… yes?

I assume these were commercially-packaged external drives. ExFAT is often a factory-default format because it is supported by MacOS, Windows and Linux. If they used other formats, then some users would have to reformat the drive, which can be a challenge for novice users.

Experts like us typically repartition/reformat new media as a part of installation, but if you’re not an expert and you just plug in a drive and it mounts, you may stop there and assume it’s all good.

As for the specifics, you figured it out. I ran across this Macworld article from 2019 pointing out that Time Machine can only back up HFS+ and APFS volumes. If you have any other format, TM won’t let you back it up.

As a general rule of thumb, all volumes that are intended for use with macOS should be APFS (for SSDs) or HFS+ (for HDDs or if compatibility with old Macs is required). Reserve the FAT, NTFS and ExFAT for volumes that you need to share with Windows or Linux systems. (e.g. I have two ExFAT-formatted devices that contain VirtualBox VM images. I use ExFAT so I can connect the drives and start the VMs on Windows and Linux computers as well as on my Mac).

Thanks David. Yes, these are Western Digital Mybooks which I’m not a fan of since many WD externals have integrated interfaces…I prefer OWC enclosure with 0TB and get robust CMR hdd in affordable capacity.
BTW- I wasn’t asked for any suggestions on these and I believe the person that setup for my friend, thought it was just Plug in and Use. I’m passing on your info to his friend, incase he is doing this for others.

I suspect it can’t be removed from excluded list because it’s EXFAT…and unless he needs to move that drive between macOS computers and Windows or Linux computers there’s absolutely no reason to keep it as EXFAT, I would back up it’s contents, erase them, and then restore the contents.

I usually buy my own enclosures (I’ve had good luck with Vantec NexStar series enclosures. I use an HX (with its cooling fan) for my Time Machine volume, and TX for my CCC backups (which are powered off when I’m not using them).

I’ve been pairing them with 4 TB Toshiba N300 drives, which are CMR, 7200 RPM and rated for 24x7 operation. The only downside to these is that they seem to run a bit warm and have relatively noisy head motion. But they seem to offer the best price per TB for a high quality drive.

WD’s USB drives are just “plug in and use”. But that comes at a cost - pre-formatted to work with the widest variety of computers - which is going to be FAT32 or ExFAT.

But that’s not ideal for any computer. If you’re running Windows, you should format it NTFS. If Linux, probably ext4. if macOS, that’s going to be HFS+ or APFS. You only want to stick with a FAT variant if you’re going to be moving the drive between multiple computers and want to maximize the number of systems that can access it.

This goes for any and all storage devices sold, not just ones sold in mass-market consumer electronic stores.