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: d

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/bfef967d4e1fa6436d2302291aa5c3267ce32a22#diff-4d79d7285bf904464d7b40fffe5c480261bac879f1926750326751163e329434 https://github.com/raspberrypi/documentation/commit/bfef967d... [2] https://github.com/scottlamb/moonfire-nvr/wiki/System-setup#disable-uas https://github.com/scottlamb/moonfire-nvr/wiki/System-setup#...