Re: Boot from USB on RPi4 8GB?

From: Mark Millard via freebsd-arm <>
Date: Mon, 31 May 2021 03:49:32 UTC
On 2021-May-30, at 16:54, William Carson via freebsd-arm <freebsd-arm at> wrote:

>> On May 30, 2021, at 4:08 PM, Mark Millard <> wrote:
>> On 2021-May-30, at 13:50, Mark Millard via freebsd-arm <freebsd-arm at> wrote:
>>> On 2021-May-30, at 10:59, William Carson via freebsd-arm <freebsd-arm at> wrote:
>>>>> . . .
>>>>> I use a USB3 SSD that has small enough power requirements
>>>>> to not require a powered hub. (I also use a 5.1V 3.5A
>>>>> power supply as part of that context.) I've never tried
>>>>> spinning rust or higher powered USB3 media.
>>> I view the power supply that I use as just giving a little
>>> more margin,  not as a way to increase what the devices
>>> total to.
>>>> . . . I'm not sure what's considered "high powered" but the Samsung tech specs say this particular model uses 5.7 W on average and 10.0 W maximum. But it does seem curious that the Raspberry PI OS will boot this disk without issue, so I don't think it's the drive. I also tried a Samsung 950 PRO using a different enclosure (QNINE NVME Enclosure, M.2 PCIe SSD (M Key) to USB 3.0 External Case), but it behaved the same.
>>> . . .
>>> Then you need to use a powered hub for that device.
>> I should have just referred to independent power. You
>> had written:
>> I'm trying to use a SAMSUNG (MZ-V7E500BW) 970 EVO SSD 500GB - M.2 NVMe, attached via the Geekworm X872 M.2 NVMe 2280/2260/2242/2230 SSD Expansion Board.
>> shows that it has its own power connector and has an image
>> that says "please power x872 via DC Jack of XH2.54 connector
>> if SSD is not recognized or low power". Later text on the
>> page says:
>> Specifications:
>> Power Supply
>> 	• 5Vdc +/-5% , Powered by Raspberry Pi USB port
>> 	• 5Vdc via DC power jack or XH2.5 connector, Extra power for the SSD
>> So, if I gather right, you need to connect a power
>> supply to the X872 and another to the RPi4B.
>> Another image says "Note: NOT recommended to use SAMSUNG SSD,
>> if use SAMSUNG SSD, please close WiFi". Later text on the page
>> says the same.
> A-ha, indeed. I just noticed that as well. I've gone ahead and ordered a supplementary power supply and a lower-power NVMe to do more testing. I'll send an update once I've received and tested them.
> Thank you for hopefully pointing me in the right direction.

I do not know if the "supplementary power supply" would be sufficient
for the existing drive to work, but it is likely necessary. Similarly
for any other drive that could require a significant portion of the
1.2A at times. (I've no clue what else you have plugged into USB or
how much power(/current) those devices take (if any). So I do not
know what to subtract from the 1.2A.)

The USB3 SSDs that I'm using are based on:

ATA Version is:   ATA8-ACS, ACS-2 T13/2015-D revision 3
SATA Version is:  SATA 3.0, 6.0 Gb/s (current: 6.0 Gb/s)

This helps explain why I've got no power problem: older
technology. Note that SATA 3.0 can be somewhat faster
than the original USB3 already, at least in some respects.

>>> lists:
>>> "Maximum total USB peripheral current draw" as: 1.2A ,
>>> which at 5.1V is 6W.

(Possibly should have listed the 6.12W figure.)

>>> That figure is the total for all USB devices attached
>>> that are not powered independently.
>>> That document also says that a 5.1V supply is required,
>>> not 5V.
>>> The power supply that the RPi folks supply is 5.1V @ 3A
>>> or 15.3W. Even the 5.1V 3.5A power supply that I use
>>> only multiplies out to 17.85W.

Mark Millard
marklmi at
( went
away in early 2018-Mar)