It's not showing up because the cache drive won't mount.
Sep 12 21:27:40 Tower emhttpd: cache TotDevices: 2
Sep 12 21:27:40 Tower emhttpd: cache NumDevices: 1
Sep 12 21:27:40 Tower emhttpd: cache NumFound: 1
Sep 12 21:27:40 Tower emhttpd: cache NumMissing: 1
Sep 12 21:27:40 Tower emhttpd: cache NumMisplaced: 0
Sep 12 21:27:40 Tower emhttpd: cache NumExtra: 0
Sep 12 21:27:40 Tower emhttpd: cache LuksState: 0
Sep 12 21:27:40 Tower emhttpd: shcmd (35): mount -t btrfs -o noatime,nodiratime,degraded -U d8be6f35-ac46-47dc-a436-08b47efeb1e5 /mnt/cache
Sep 12 21:27:40 Tower kernel: BTRFS info (device sdb1): allowing degraded mounts
Sep 12 21:27:40 Tower kernel: BTRFS info (device sdb1): disk space caching is enabled
Sep 12 21:27:40 Tower kernel: BTRFS info (device sdb1): has skinny extents
Sep 12 21:27:40 Tower kernel: BTRFS warning (device sdb1): devid 1 uuid e6e2a765-5a51-4852-8f25-ad8b47d3de4b is missing
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Sep 12 21:27:40 Tower kernel: BTRFS warning (device sdb1): chunk 4384096256 missing 1 devices, max tolerance is 0 for writeable mount
Sep 12 21:27:40 Tower kernel: BTRFS warning (device sdb1): writeable mount is not allowed due to too many missing devices
Sep 12 21:27:40 Tower root: mount: /mnt/cache: wrong fs type, bad option, bad superblock on /dev/sdb1, missing codepage or helper program, or other error.