[Solved] APFS Time Machine Volume won't add secondary disk
I have a 2 hard disk array with two volumes, one HFS (5 TB) and one APFS (Time Machine, 3 TB). Some things happened and I ended up with a split mirror. To fix this, I initialized one of the disks, added it as a secondary disk for the HFS volume, and let it rebuild. That went fine. I attempted to do the same with the APFS volume, but that didn't work.
I can add the secondary disk to the APFS volume, which completes successfully according to the SoftRAID log, but the volume still appears as missing a secondary volume (I cleared the secondary disks before doing this), and the secondary disk shows too much available space. The primary disk has 134 MB available, while the secondary still has 3 TB.
As this is only for Time Machine I don't care that much, but would prefer to avoid wiping the volume.
After a couple of reboots, the APFS volume added the secondary drive correctly and is now rebuilding. Unclear what if anything I did.