Actually, they have a usb hub built in. You can plug two more into the back of each
Thank you @Alexey
@andrew2.hart, they do exist, but they are not part of my setup, I do not use them.
That would add additional complexity that I was talking about. Without it they can work quite well.
Fortunately I have a couple of my book duos (they are really good imo!)
Here you can see an “elements” plugged in next to a “duo”
: Bus 004.Port 001: Dev 001, Class=root_hub, Driver=xhci_hcd/6p, 5000M
ID 1d6b:0003 Linux Foundation 3.0 root hub
|__ Port 001: Dev 002, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
ID 1058:25a3 Western Digital Technologies, Inc. Elements Desktop (WDBWLG)
|__ Port 002: Dev 003, If 0, Class=Hub, Driver=hub/3p, 5000M
ID 1058:25f9 Western Digital Technologies, Inc.
|__ Port 003: Dev 004, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
ID 1058:25f6 Western Digital Technologies, Inc.
I think this means that you are using the duo’s hub
Perhaps if I plug in another elements into the back of the duo …
/: Bus 004.Port 001: Dev 001, Class=root_hub, Driver=xhci_hcd/6p, 5000M
ID 1d6b:0003 Linux Foundation 3.0 root hub
|__ Port 001: Dev 002, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
ID 1058:25a3 Western Digital Technologies, Inc. Elements Desktop (WDBWLG)
|__ Port 002: Dev 003, If 0, Class=Hub, Driver=hub/3p, 5000M
ID 1058:25f9 Western Digital Technologies, Inc.
|__ Port 001: Dev 005, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
ID 1058:25a3 Western Digital Technologies, Inc. Elements Desktop (WDBWLG)
|__ Port 003: Dev 004, If 0, Class=Mass Storage, Driver=usb-storage, 5000M
ID 1058:25f6 Western Digital Technologies, Inc.
See, it appears on the hub the same as the duo?
I’m willing to be educated on this but how does the elements and duo appear on a completely separate tree to a hp usb stick plugged into the same slot?
I completely agree that there is an internal USB hub inside My Book duo, since there is only one USB output and two disks in there, there is no arguing there.
What I I’m saying is that I don’t use additional USB ports behind for connecting additional external HDDs, because that would add additional complexity and push it to the limits and then unwanted scenarios can happen. My logic is to keep it to minimum, not maximum.
However I’m sharing what my setup is about that I didn’t had any issues in long term. If you are using the same My Book Duo case with even more disks on it and sharing that is working for you, that’s even better and a couple of more points to USB drives 
What stays is that cheap products makes them look bad, it’s not a rule.
Im not using the my book duos at the moment. I prefer them to elements because they have an idle fan that can kick in if needed. I guess I just don’t need the 32TB
Want to share a small anecdote, not reading any previous posts.
i knew a guy who got a HDD farm for other projects in normal house hold.
He praises USB, BUT it has to be a server hardware, like Supermicro’s brand.
He claimed there where no problems with his USBs, and he keept the HDDs on them all the time. So its really the quality of product and software, not the standard itself i guess.
the main takeaway of ‘why not recommended’ is because there are a million options for USB out there, some bulletproof and well done, some a person in china found a box of chips and put them in a 3d printed case and sold them to you with zero testing are then plugged into the lowest priced item you could find that day running an OS that barely tested the hardware its on let alone 100 USB hard drives plugged into it.
So to avoid headaches, ‘not recommended’ is the answer.
Correct. “just don’t” is a sufficient response to a topic title question, because it’s a correct intuition, and intuition is we know it is simply a compressed experience, that is often difficult to articulate – but I’ll bite and elaborate on some reasons, in no particular order:
- USB-Sata bridges are SHIT. All of them? Yes. But… but… some are maybe OK? No. They are exclusively used in consumer products. There are no downtrickle from enterprise. They are universally shit. Their design document is in its entirety "Make it cheap. No, cheaper. Even cheaper. Keep going. Good boi! Now shave off few more cents. ". They drop under sustained IO, mishandle NCQ, or handle error recovery in a way even their maker has no idea bout – because it wasn’t part of the spec.
- Very rarely there is a side band channel to pass through temperature let alone smart data. You are flying blind.
- USB links reset on transient errors. Radom bus resets are bad news for your data.
- Shit power delivery. Brownouts cause data lost/controller hangs/disk hangs.
- Shit thermal design causes overheats/hangs/dropped packets/ see about
- Shit EMC design – you pet the cat nearby – bam, controller reset.
- Firmware stability: No thought was put into it. It was copied from reference design example, and never modified or tuned.
- If you use the HUB – (as you can see above, most devices do internally, because it’s easier) here is a fresh new can of gooey worms for you:
- Hubs oversubsribed to insufficient power budget. Yes, even if you use external power supply for your disk – some, notably WD BOOK, draw FULL power (500mA) from a usb port. Yes, really. Yes, it’s dumb. yes, they still do it. Remember – consumer shit. Don’ buy it. But people keep buying. Sigh…
- One unstable device in the whole topology can lead to root reset – resetting the whole tree.
- Hubs can reorder USB bulk transactions under congestion. This leads to kernel I/O errors.
- You can forget about UASP. It’s universally broken on cheap hubs. If you don’t disable it – data loss. I you disable it – performance loss. Pick one.
- Because interrupts are shared – storm on one port degrades timing on all port, avalanching the issue.
- Cables are shit. Oxidation/intemittne connection/ resets.
- …
Forget about USB disks please in any context outside of emergency data transfer.
Ok Ill graceful exit the lot
I’m running 2 Mybooks via USB without any issues, but what I can tell, is, multi HDD external cases for like 4 or 8 HDDs are crap. I had one from icybox and orico, both weren’t able to get past 250mb/s even though they were promoted with UASP, neither on windows nor on linux it was working. Also these controlers suck at high I/O (if not already told here). Fro cloning I bought an 5.25" 4 Bay hot swap bay, printed a case, and run it via esata, with much more and reliable speed.
If you like eSata over USB…I’m selling mine due to reliabilty issues.
I will never use esata on linux again
Whoops broke some rule…