ArunawayNERD

So those commands actually failed, but the error messages were enough to put me on the right track to figuring it out. Both the SSDs are now formatted and operating in the cache pool. Thank you so much for your help

For anyone else with the same issue who might come across this in the future here was my issue (/journey lol)

So both blkdiscard -f /dev/sdb and blkdiscard -f /dev/sdc failed with the same error message BLKDISCARD: /dev/sdb ioctl failed: Input/output error. At the end of system log (amongst a bunch of other error/logs) was the line device reported invalid CHS sector 0

When googling that error I was coming across a lot of posts about checking the sata cables, the connections, the sata ports, etc. That triggered in my mind that I had plugged these SSDs into sata port 4 and 5 on my motherboard. I also vaguely remember seeing some bios setting specifically for ports 4 and 5. Sure enough there was the setting "OnChip SATA Port 4/5 Type" which was defaulted to "IDE".

I switched it to "As SATA", saved, and exited. Once Unraid came up I tried formatting the drives again and it succeed

Thanks again for the help