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M1 MBA will not mount two Thunderbolt drives at same time on battery.

M

Mike Boreham

macrumors 68040
Original poster
Aug 10, 2006
3,953
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UK
I have had my M1 MBA for nearly two years but only just tried to do this for first time, and discovered that it won't.

Drives are Envoy Express TB enclosure with 2TB Sabrent NVMe blade, and Orico TB enclosure with 4TB blade. Note these are pure TB drives and cannot connect to a USB-C port unless it is TB3, TB4 or USB4 protocol. This means they have to be plugged in to the two TB3 ports on the MBA, hence MBA has to be running on battery.

I can mount either of them connected to either port, but not both at the same time. Tried different leads rebooting etc.

I have another M1 MBA at home and will try the same out on that. Meanwhile interested to hear from anyone who has tried the same.

At home I have OWC powered Thunderbolt hubs so no problem connecting two or more drives at home, but not on the road without this, although I can work around the limitation.
 
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jdb8167 said:
Do you have any power requirements specs on the drives? It seems likely that you are exceeding a power draw limitation of the MBA.
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Thanks. Yes that would seem to be the case but there weren't any warnings, such as I have had at other times with USB devices. Also I thought Thunderbolt ports had a lot of power available for drives. OTOH Thunderbolt drives probably need more power since they transfer data faster and run hotter.

Will see if I can track down power requirements for the drives. I also have a Satechi USB-C power meter which might reveal something.

it is possible that this M1 MBA is faulty which I can check when get home next week and can check my other machine.
 
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You can also by an adapter that has a power pass-through port on it so that you can power the MacBook at the same time as you're using the two ports.
 
BanditoB said:
You can also by an adapter that has a power pass-through port on it so that you can power the MacBook at the same time as you're using the two ports.
Click to expand...
Thanks but not sure I understand that. The adapter carrying the power must plug into one of the ports, leaving only one free for a TB drive. There are lots of adapters which have USB-C ports but none of them support Thunderbolt.

Will be delighted to be proved wrong if you can send a link. I have looked hard for such a device.
 
jdb8167 said:
Do you have any power requirements specs on the drives? It seems likely that you are exceeding a power draw limitation of the MBA.
Click to expand...
I have put a Satechi USB-C power meter in series with my 4TB Thunderbolt drive.

At idle the drive draws 5V 0.58A
While being written to it drew 5V 1.68A
I saw a brief spike on connection of 5V 1.21A

These are all well within the min port power spec for drives of 15W for TB3/TB4 from here. So going off the excess power explanation.
 
Mike Boreham said:
Thanks but not sure I understand that. The adapter carrying the power must plug into one of the ports, leaving only one free for a TB drive. There are lots of adapters which have USB-C ports but none of them support Thunderbolt.

Will be delighted to be proved wrong if you can send a link. I have looked hard for such a device.
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You're right. I was thinking of Apple's Multiport Adapters, but they only feature power input and have no other Thunderbolt ports. That would leave you with using your Thunderbolt docking station.

By chance, have you contacted Apple Support to see what they can tell you? It'd be interesting to hear what they come up with.
 
BanditoB said:
By chance, have you contacted Apple Support to see what they can tell you? It'd be interesting to hear what they come up with.
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I am waiting until I can test my other M1 MBA at home. But meantime I have heard from two other M1 MBA owners: one has the same problem as me and the other one doesn't. They are using different Thunderbolt drives from me, so I am leaning towards an explanation related to some subtle compatibility issue of the drives, or it might be some a very marginal situation which some machines cross and some don't.
 
Can you mount the offending drive first then the drive that mounts without issue?
 
Cabin said:
Can you mount the offending drive first then the drive that mounts without issue?
Click to expand...

Neither drive is the offending drive. Either will mount from either port, then the second one won't.

I have now tested my second M1 MBA and it is exactly the same.

I have also more info from the other two owners who have tested for the issue:

Three out of four Macs have the same problem.

The one that didn't was tested with packaged enclosure + NVMe (OWC Envoy and Sabrent Q) while the three that have the problem have only been tested with roll-your-own drives, separate purchase of enclosure and NVMe by different manufacturers. May be a red herring but still a fact.
 
I was reading in another thread regarding the power supplied by the built-in TB ports, and, if I recall correctly, whatever gets plugged in first gets 15W and whatever gets plugged in second is limited to 7.5W. Your experience makes it sound like this is probably right.
 
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BanditoB said:
I was reading in another thread regarding the power supplied by the built-in TB ports, and, if I recall correctly, whatever gets plugged in first gets 15W and whatever gets plugged in second is limited to 7.5W. Your experience makes it sound like this is probably right.
Click to expand...
Thanks...yes could be. The current draw measurements I posted above are close enough to 7.5W to explain.
 
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