dizzo
Posts: 7
Joined: Mon May 14, 2018 12:31 am

USB Booting Question

Mon May 14, 2018 12:37 am

I've searched through the topics and I can't seem to find a simply answer to this issue. If someone knows a thread that answers it please direct me.

I have a Model 3b+ with a powered 1TB external HDD attached. I'd like to have the pi boot from that drive since my understanding is that it will give better performance

I used the SD Card Copier to copy my SD card over to the HDD, that seems to have worked fine. I see the exact same partitions with at 900+ GB "data" partition.

As far as I can tell the pi is still booting from the SD card, which makes sense given the boot order the pi generally operates from.

So my ultimate question is; what do I do to erase Raspbian from the SD card safely without also deleting the stuff (the bootloader I think) that still needs to be on the SD card.

Thanks.

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rpdom
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Location: Chelmsford, Essex, UK

Re: USB Booting Question

Mon May 14, 2018 8:25 am

With the 3B+ you shouldn't need the SD card at all. There will be a few seconds delay while the Pi checks to see if there is a valid SD card, before moving on to boot from the USB device.

W. H. Heydt
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Location: Vallejo, CA (US)

Re: USB Booting Question

Mon May 14, 2018 2:29 pm

dizzo wrote:
Mon May 14, 2018 12:37 am
So my ultimate question is; what do I do to erase Raspbian from the SD card safely without also deleting the stuff (the bootloader I think) that still needs to be on the SD card.
Shut down the Pi. Remove the SD card. Restart the Pi. That's it.

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piglet
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Re: USB Booting Question

Mon May 14, 2018 2:38 pm

rpdom wrote:
Mon May 14, 2018 8:25 am
With the 3B+ you shouldn't need the SD card at all. There will be a few seconds delay while the Pi checks to see if there is a valid SD card, before moving on to boot from the USB device.
I never got this to work reliably on a 3B with a WD Foundation Edition Pi drive. Maybe 1 time out of 10. Are things fundamentally different on a 3B+? I ended up having to use a small SD card just to get reliable booting.

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rpdom
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Location: Chelmsford, Essex, UK

Re: USB Booting Question

Mon May 14, 2018 3:02 pm

piglet wrote:
Mon May 14, 2018 2:38 pm
I never got this to work reliably on a 3B with a WD Foundation Edition Pi drive. Maybe 1 time out of 10. Are things fundamentally different on a 3B+? I ended up having to use a small SD card just to get reliable booting.
Yes, the 3B+ has some improvements in the boot ROM that support more devices. I couldn't get a 3B to boot from my USB disk, but it worked first time on a 3B+

k-pi
Posts: 920
Joined: Sun Feb 12, 2017 1:46 pm
Location: Upper Hale, Surrey, UK.

Re: USB Booting Question

Mon May 14, 2018 3:33 pm

I've been booting my 3Bs & 3B+ from pendrives & external disks (as long as they get enough power) without any problems, :)

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HawaiianPi
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Joined: Mon Apr 08, 2013 4:53 am
Location: Aloha, Oregon USA

Re: USB Booting Question

Mon May 14, 2018 6:00 pm

The main issue with mechanical hard drives is the spin-up time. The Pi boot loader waits 2 seconds for the drive to get ready, and if it takes longer than that it won't be seen and boot will fail. Having only the bootcode.bin file on a FAT32 SD card with another file named "timeout" will increase the wait time and possibly fix the problem.

If you want pure, no SD card boot, and you suspect a wait time issue, then adding "program_usb_boot_timeout=1" to config.txt on a Raspbain SD card and booting it once will set an OTP bit that tells the system to wait 5 seconds. Note this is different from the OTP bit that enables USB boot, so on a Pi3B you'd need to set both bits for USB boot with the additional wait time (the 3B+ has USB boot enabled by default).
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