*Finally* found the answer. The case was, if you'll recall, that I had replaced a pair of older, smaller drives with a couple of 8TB SATA drives, and made it RAID1 using the PERC firmware. I was then going to wipe the drive. First, the old ones turned out to be SAS, no SATA. I had tried shoving it into a similar Dell, which I regularly use for shoving SATA drives in, and copying over the network, then putting them (larger drives) in place of the ones they were replacing on other servers. This just wouldn't show as /dev/sdx, the way the SATA did.
The solution: a script I found on the 'Net lsi.sh, which depends on you having MegaRaid on the box, shows the four drives, but that one was listed as "unconfigured good". What I needed to do was use MegaCLI64 to first display foreign configurations... and regardless of the other three SATA drives, did show only one, and that was from this SAS drive. I then did a clear foreign configuration. After that, I could use PDMakeJBOD, and all is wonderful.
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