I have a 2TB WD portable drive I use as my day-in, day-out archive of photos, music, etc.

I bought a 4TB WD portable drive to back THAT one up to.

(When I say "portable", I mean they're the deck-of-cards style, no external power needed, both use the ten-pin MICRO B style connection).

I only have one USB port on my machine, so I use an Anker hub to connect multiple devices.

Lately, the larger drive won't stay mounted during synchronizing activities. It will go for a while, and then I'll hear it dismount and remount. (It's happened twice while I've been typing this).

This happens when my PC is plugged into multiple places, so I don't know that it's a power issue (unless my power brick isn't drawing enough).

Any suggestions?

ThanksMy guess is that you need a powered hub in order to supply enough power for both drives.Was wondering that. It worked well enough at one point that I conducted an initial backup. How much do PCs vary in the amount of power they supply via the USB port? (Two questions - How much do they vary from PC to PC, and how much can one PC vary from session to session/moment to moment)?You've opened a can of worms asking about USB Power! Very complicated stuff, but given your symptoms it definitely seems to be an issue with power.

For USB Type-A Ports, According to the specs, A single USB 2.0 Port can supply up to 500mA. a single USB  3.1 Port can supply up to 900mA. More power can be supplied if the host device and the device being plugged into support appropriate Power Delivery specifications and "agree" on a current limit.

With respect to an unpowered hub, this would mean that all devices plugged into a hub must "share" the power being provided by the single USB Port on the PC/device the hub is CONNECTED to. From what you've stated it sounds like that could be part of the issue. Even if the Hub is able to draw extra power from your SYSTEM via Power delivery specs, (hard to know for sure without a little USB Power dongle) it may be that two drives are simply beyond what that full current from one port can supply.
Do you think hubs go "bad" over time?

As I said originally, I HAD done a sync through this hub - and now it won't stay mounted.

Now I'm having trouble mounting USB sticks.

Think the contacts get corroded, or what?Yes they do go bad...especially the cheap ones.
Personally i'd never buy an external that doesn't have an A/C power adapter but thats just me.PS...if it wont even take a stik right now dont risk data loss usin the HDD's on it.Yeah, I need something I can keep on the road with me. In my experience, Anker's stuff is usually pretty good. Do you disagree?

BTW I bought a powered hub (Anker, natch) and it did the backup just fine, between the two drives.

ThanksI have an Anker hub that is the same as the one pictured but has more sockets(7) and has an AC Adapter. I've not actually used the AC Adapter and not yet had any issues with External drives (powered from their own AC Adapters) or USB Flash Drives, and I've in some cases had something plugged into every port.Yeah, that sounds like the one I just bought.

I wonder, too, if "house" power varies - even though the brick should regulate that, I've noticed sometimes when I'm plugged in at hotels, things don't charge as quickly or mount as easily as when I'm back in my apartment.