Addded a 60 GB msata SSD (DOgfish Shark) via Geekworms X850 mSATA expansion board yesterday then cloned my SD card to the drive using RPI-Clone. (Have also added their X735 power management/cooling board and popped it all in one of their metal cases)
Rebooted the Pi(with the SD card still in) and then confirmed that I was indeed now using the SSD rather than the SD card .
When booting from SD power light is red, green light flashes then goes out device boots and runs from SSD (blue light disk activity flashing)
When SD card removed and Pi booted power light is red, green light doesn't flash and blue light stays solid
NB understand that running RPI-Clone with the -l option means it does the initial boot from the card mounts the USB drive then leaves the SD card unmounted .
Posted over at the main Raspberry Pi forums as well however given that this "General " forum is listed as "General discussion about Pi-hole, Raspberry Pi's, or anything else." then thought I would ask the erudite people here as well
I'm suspecting there may just be an issue with the SSD (possibly power related??) as I just cloned the SSD back to a fresh SD card but without the -l option (ie leaving the SD card bootable). Verified it would boot & run from the SD card then recloned back to the SSD this time without the -l option.
Powered down, removed SD card and just sits there as it did previously.
Power off i, insert original SD card and it all boots up and mounts and runs from the SSD as previously.
Guess it's not too march of a hardship to leave it like this given once the Pi is up and running the SD card can be removed safely given it's not mounted.
Not all devices can successfully boot a Pi 3B or 3B+. Sometimes this is due to timing problems. If you have a spare SD card, you can copy just 'bootcode.bin' from a working SD card and add an empty file named 'timeout' to an otherwise blank SD card, then use that to boot the Pi. With that setup the Pi will load the bootcode from the SD card, wait a bit longer than usual, then try Ethernet boot, then USB mass storage boot.
Note that the card needs to be FAT32 (or FAT16 for really small older cards), not ExFAT. Since 64GB and larger cards are ExFAT by default, these would need reformatted to FAT32 first.
The advantage of the bootcode.bin only method is that there is less chance of corrupting the SD card, and if it does get corrupted you've not lost anything - just copy bootcode.bin back on and add the timeout file again.
so having had a think about this I think I'm going to leave it "as is" if only for the most basic reason, "it's working" lol
Actually what I've also done is set up a cron job to run " rpi-clone -q -l mmcblk0" every night so that the SSD (64Gb) is cloned back to the SD card (also 64GB) as a backup.
if needs be its relatively simple to pop the SD card back into my laptop , rename "cmdline.txt" to cmdline.txt.ssdboot then rename "cmdline.boot " to "cmdline.txt" then boot the Pi back from the SD card rather than mounting the SSD