I've been thinking for a while that I should contemplating maintaining a local backup of our business OneDrive data (circa 600GB). Can anyone provide any recommendations in this respect?
Is it feasible to couple a removable 4TB SSD drive to my RT3200 (without frying my RT3200's USB port), e.g. something like:
this:
or this:
I already use rclone to copy scanned PDF files to OneDrive, and I'm supposing I can use rclone in the other direction, to maintain my local backup.
Any reason you're not getting/building a NAS instead?
SSDs draw little current (at least, in contrast to HDDs). And it should not be possible to fry the USB port with a decent device; in the worst case, the router will cut the current if the device draws too much. In case of trouble, a powered USB hub should be enough.
I'm open minded. I suppose a benefit of NAS is higher transfer rates given ethernet versus the USB 2.0 limitation on the RT3200 and facilitation of HDD use given own power supply.
Drawback is increased power consumption and physical space requirements:
Why not consider building your own? Provided the files on network storage are something like small text documents and PDFs, and infrequently accessed, you can simply repurpose an old machine, operate at low power settings. Or you can even base it on hardware that's recommended for x86 OpenWrt, add some disks and install TrueNAS.
If it's going to be more heavy duty, then you can't get around power consumption, ether you go prebuilt or custom build.
Sure, using USB 2 would be slow especially if you consider SSD drives.
Keeping a separate NAS simplifies the role of each device.
Well, I have a 3-bay NAS (Qnap TS-351) for backup, which I only turn on monthly when I do the monthly backup of my PC. There is no real reason to keep NAS on all the time, if its purpose is only a periodical backup.
(Ps. cloud OneDrive gives you cloud recycle bin etc. in any case, so daily backups are likely unnecessary(?))
even cloud providers recommend 3rd party backups https://www.backblaze.com/blog/the-3-2-1-backup-strategy/ (at least the serious ones 
)
WD NAS is no good.....previously they just stopped to support some old models and lots of people were angry about that.
You can think about getting a Terramaster 2 bay NAS (those with Intel CPU), replace the internal USB boot drive you can already boot OpenWrt and make use of the dual NIC to build OpenWrt router, then you can freely use the 2 bays for storage and the RT3200 as AP.....
I put together an RT3200 with a Samsung 1TB USB SSD for my sister almost two years ago, to replace her ancient Apple AirSomething router+backup system with like-for-like capabilities. The Apple router-thing had a 600 MB spinning rust drive, and it was less than half full after 11 years of use (I break out in cold sweat just thinking of her relying on it as a backup), hence the 1TB SSD size.
I set the RT3200 up with Syncthing, had her install Syncthing on her Apple laptop and she's been off to the races ever since (seems to work much better than her old Apple backup thing, which was fiddly and needed constant resets and restarts). I also put sqm on the router, running cake, which fixed her video call/streaming issues. Next update will probably get adblock with a small list to enhance privacy a bit.
She only has about 4 total devices (laptop, printer, tv, phone) on her network, so no lack of CPU to run all of that. I did put a power meter on it, but neglected to write anything down, I do recall it was just fine with the USB drive.
Here in The Lab, my RT3200 has a Toshiba Canvio 4TB USB Spinning Rust drive (used to check configs before I roll them out to sister's box). Apparently no issues with power, although I have yet to put the meter to it.
