Limitation on number of external drives - 14 max on 2 hubs / 1 controller?

Got a bizarre one for you. Wondering if you have encountered something like this before.
Before I go chasing off into the Web’s Garden of No Return…

My system (“GORDON”): HP Pavilion DV7 17” notebook running Windows 10 x64 Version 1703
16GB. 2 x 1TB internal HD.

Fully updated. SFC scanned. DISM checked. Norton / Malwarebytes.

Renesas USB 3.0 USB Host Controller. Driver updated 4-17-2017 Version: 10.0.15063.296

Two USB 3.0 ports on the laptop:

#1 Anker 13-port hub
4 x Seagate 4TB external HD
2 x Seagate 8TB external HD
1 x WD 4TB external HD
1 x HGST 8TB external HD (Inateck case)

#2 Anker 10-port hub
2 x Seagate 5TB external HD
1 x Seagate 4 TB external HD
1 x WD Passport 2TB external HD()
2 x Seagate Portable 4TB external HD(
)

(*) Bus powered. All others have wall-wart power adapters.
HGST is only drive using a 3rd party enclosure.

I have no problems moving massive files among any of these drives, often 4 or
more multiple operations at once (using Beyond Compare 4).

Issue: I cannot seem to add a 15th drive via either of the Anker hubs.

Started noticing this a month or so ago trying to add a SanDisk 256GB thumb drive for
routine file transfers. SanDisk worked fine on two other systems but would not mount on GORDON.

I may not have noticed this for a while because my system image backup job mounts and then
dismounts its target drive when done. I removed the DISMOUNT part of the procedure to diagnose a different issue and it has remained that way.

Transfers piled up, so I needed more than 256GB. I just moved to using a Seagate 2TB portable HD.
As with the SanDisk, Windows gives the “ding” tone which usually signifies HD connection,
but the drive does not show up anywhere including in DISKMGT.

I then attached this drive to a Manhattan 10-port USB 2.0 hub (to one of
the two built-in USB 2 ports) and it worked fine there (although 3x-4x slower).
Whew! It was able to draw enough power via USB 2!

I had briefly thought there was an issue with the 24 drive letter limit but its appears there
are 4-5 drive letters available.

Next I took the two mounted Seagate portables off-line (hub #2) and now the new Seagate
portable 2TB mounts on the Anker 13-port hub (#1)!

And with two slots freed up, the SanDisk 256GB thumb drive now also mounts: 2
removed – 2 added! Still at 14!

Therefore it appears there is a 14 total external drive limit, I presume on the USB
3.0 controller itself(?).

I did notice that the Anker hubs must not be receiving a signal from the controller
because the 15th drive’s port LED does not light up.

Very interesting.

This perhaps also explains an issue from a year ago when I had trouble connecting a Vantec
NexStar HX-4 drive array (4 bays). That probably pushed things over this now apparent 14 drive limit much sooner than happened in the current situation.

My next system will be an All-In-One (4xUSB 3.x at least), perhaps even a workstation
version, or a maybe even a desktop, but I would certainly like to determine, in
advance, if this issue could crop up again.

I realize this issue is not a problem with the Anker hubs themselves but perhaps your
people have seen something like this before.

Surely this must be a very rarely encountered issue; not sure that manufacturers or support
people would even be aware of it or know how to find the information.

Always useful information to be had.

Thanks

—JCN

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Are the “spare letters” actually available? They could be reserved for other uses (card readers, hidden partitions etc) .
The other thing is maybe the drives are trying to use the same letters are each other. So you may have to manually assign letters to each drive. This can be done in disk management.

IT could also be a power issue if each of your external drivers is drawing power from the hubs. If the drive is not able to draw enough power, then it wont mount correctly on the pc. (regardless of lights on it)

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