I am trying to create a new cache pool formatted with btrfs. When I try to format the drives after starting the array, it doesn't work. Checking unRAID logs shows this:

Mar 23 17:40:12 Tower kernel: mdcmd (44): nocheck pause

Mar 23 17:40:12 Tower kernel: md: recovery thread: exit status: -4

Mar 23 17:40:13 Tower emhttpd: creating volume: newcache (btrfs)

Mar 23 17:40:13 Tower emhttpd: writing MBR on device (nvme3n1) with partition 1 offset 2048

Mar 23 17:40:13 Tower emhttpd: shcmd (572798): sfdisk --quiet --label dos /dev/nvme3n1 <<< 'start=2048'

Mar 23 17:40:13 Tower kernel: nvme3n1: p1

Mar 23 17:40:13 Tower kernel: nvme3n1: p1

Mar 23 17:40:13 Tower emhttpd: shcmd (572799): udevadm settle

Mar 23 17:40:13 Tower emhttpd: shcmd (572800): /sbin/wipefs -af --lock /dev/nvme3n1p1

Mar 23 17:40:13 Tower root: wipefs: error: /dev/nvme3n1p1: probing initialization failed: No such device or address

Mar 23 17:40:13 Tower emhttpd: shcmd (572800): exit status: 1

Mar 23 17:40:13 Tower emhttpd: shcmd (572801): /sbin/blkdiscard /dev/nvme3n1p1

Mar 23 17:40:13 Tower root: blkdiscard: cannot open /dev/nvme3n1p1: No such device or address

Mar 23 17:40:13 Tower emhttpd: shcmd (572801): exit status: 1

Mar 23 17:40:13 Tower emhttpd: writing MBR on device (nvme0n1) with partition 1 offset 2048

Mar 23 17:40:13 Tower emhttpd: shcmd (572802): sfdisk --quiet --label dos /dev/nvme0n1 <<< 'start=2048'

Mar 23 17:40:13 Tower kernel: nvme0n1: p1

Mar 23 17:40:13 Tower kernel: nvme0n1: p1

Mar 23 17:40:13 Tower emhttpd: shcmd (572803): udevadm settle

Mar 23 17:40:13 Tower emhttpd: shcmd (572804): /sbin/wipefs -af --lock /dev/nvme0n1p1

Mar 23 17:40:13 Tower root: wipefs: error: /dev/nvme0n1p1: probing initialization failed: No such device or address

Mar 23 17:40:13 Tower emhttpd: shcmd (572804): exit status: 1

Mar 23 17:40:13 Tower emhttpd: shcmd (572805): /sbin/blkdiscard /dev/nvme0n1p1

Mar 23 17:40:13 Tower root: blkdiscard: cannot open /dev/nvme0n1p1: No such device or address

Mar 23 17:40:13 Tower emhttpd: shcmd (572805): exit status: 1

Mar 23 17:40:13 Tower emhttpd: /sbin/mkfs.btrfs -K -f -d raid1 -m raid1 /dev/nvme3n1p1 /dev/nvme0n1p1

Mar 23 17:40:13 Tower emhttpd: btrfs-progs v6.17

Mar 23 17:40:13 Tower emhttpd: See https://btrfs.readthedocs.io for more information.

Mar 23 17:40:13 Tower emhttpd: mounting /mnt/newcache

Mar 23 17:40:13 Tower emhttpd: shcmd (572806): mkdir -m 0666 -p /mnt/newcache

Mar 23 17:40:13 Tower emhttpd: newcache: no pool uuid

Mar 23 17:40:13 Tower emhttpd: shcmd (572807): rmdir /mnt/newcache

Mar 23 17:40:13 Tower emhttpd: newcache: mount error: wrong or no file system

Mar 23 17:40:14 Tower emhttpd: Restarting services...

Mar 23 17:40:15 Tower emhttpd: shcmd (572810): /etc/rc.d/rc.samba reload

Mar 23 17:40:15 Tower emhttpd: shcmd (572814): /etc/rc.d/rc.avahidaemon reload

Mar 23 17:40:15 Tower avahi-daemon[2571]: Got SIGHUP, reloading.

Mar 23 17:40:15 Tower kernel: mdcmd (45): check resume

Mar 23 17:40:15 Tower kernel: md: recovery thread: recon P ...

Try completely wiping the devices with

blkdiscard -f /dev/nvmeXn1

Then reboot and try again.