Yes, I have a Pi4 booting off a SSD on a USB-SATA bridge. No SD card installed. This graduated from beta about a year ago. [1]

Btw, since you brought up USB: disable UAS [2] when using cheap USB-SATA bridges! UAS is regularly recommended for performance reasons, but I've gotten block-level errors (eg those below) and filesystem corruption with UAS multiple times and never with UAS disabled. I've seen enough similar reports on the Internet to think it's better to just disable UAS.

    Sep 22 17:26:01 nuc kernel: sd 4:0:0:1: [sdb] tag#2 uas_eh_abort_handler 0 uas-tag 3 inflight: CMD OUT
    Sep 22 17:26:01 nuc kernel: sd 4:0:0:1: [sdb] tag#2 CDB: Write(16) 8a 00 00 00 00 01 4d b4 c4 00 00 00 03 b0 00 00

The Linux kernel has explicitly disabled UAS for some of these chipsets, but clearly not all of the offending ones. I'm not sure what you'd have to do to be confident your chipset is safe. I just don't think it's worth it.

[1] https://github.com/raspberrypi/documentation/commit/bfef967d...

[2] https://github.com/scottlamb/moonfire-nvr/wiki/System-setup#...

https://github.com/pftf/RPi4 allows you to store the UEFI firmware on the sd card. This enables you to not only boot from USB, but also PXE and even ISCSI

UEFI on an sd card -- that is so cool.

Yes - on the rpi4s, you can enable booting from usb devices directly using raspi-config, although raspbian is only 32 bit, so I wound up having to do a weird dance of using raspbian to enable usb boot and then installing ubuntu on the drive to get a 64bit OS

FWIW Raspbian has a 64 bit version in beta https://downloads.raspberrypi.org/raspios_arm64/images/raspi... the base image is outdated but you can full-system update from that point.

I'm the same way though, I just use a more typical distro unless there is something I need the standard toolset for.

Yeah, I’d seen the beta, but it looked like an early effort shortly abandoned - it didn’t inspire a lot of confidence.

Edit: although giving it a second glance, it looks like there’ve been a few updates: https://downloads.raspberrypi.org/raspios_arm64/images/

Note that Raspberry Pi OS also has a 64-bit beta version, and it's been extremely stable for me for months now.

I'll chime in that I've been using 64-bit raspberry pi OS for at least 8 months now and I haven't had any issues with it, other than a small snafu when I first tried to get Wireguard up and running but some of the base packages didn't yet support 64-bit OSes (I think?). That issue has since been fixed, I can happily report.

Be careful trying to boot 64 bit Ubuntu off a hard drive. You have to uncompress the kernel, or the boot will hang.