Transferring files from portable hard drive to iCloud

Jerry Dammers wrote: ... I am nervous about portable hard drives as they do not always mount and I didn't consider them a long term primary solution,

I'm using this with my laptop:

Picture's from Amazon. 2 TB SSD, weighs about an ounce, and I get about 900 MB/s on my M3 PowerBook and on my M1 Air. $150. Easy to carry around. And everything on it is backed up somewhere else.

I have four Samsung running as backups (TimeMachine and CCC) on two Mac's. Three are T7's and one is a T9. Haven't had any trouble with them not mounting.(knock on wood) I also have 1 T9 and one old T7 I use for other non essential backups since I have started to removing everything that I had on different clouds. I don't use iCloud that much and disabled Desktop and Documents feature and only use Sync this Mac on both MBP. If you format them with Erase and reformat a storage device in Disk Utility on Mac - Apple Support (CA) then there shouldn't be any trouble with them not mounting unless the exteral already has problems.

Jerry Dammers wrote: ... Is it possible to transfer the contents from my portable hard drive to iCloud via my MacBook Pro, without having to first download all the content to my Mac?

I'm not sure that your question as been addressed. I'm pretty sure that the answer is "No." I tried dragging a 50 GB folder from an external drive to my iCloud Drive, and my Mac's internal drive's "used" value went up accordingly. In neither case did I have "Optimize Storage" turned on, so it switched that on, and it looked the same.

I use two hard drives. Well, actually, I have more than that.

iCloud is not a backup solution. It is a synchronization service. If you are going to back use other cloud solutions such as Google Drive, Mega or OneDrive.

Typically for backing up multiple devices, for family sharing, and for keeping full resolution photos in iCloud with optimized versions on the Mac. The Mac Pro also can be configured up to 8TB.