On Tue, Oct 6, 2020 at 4:06 AM Kenneth Emerson
[off-list ref] wrote:

It's been several years since I asked and received help on this list.
Once again, I find myself in a bind.  I have accidentally destroyed
one of my disks in a set of 5 4-TB drives set as RAID6. When I
rebooted 2 of the three arrays rebuilt correctly; however, the third
(largest and most important) would not assemble.  I thought, even
though I had lost one drive, I could rebuild the array by substituting
a new, partitioned drive but I cannot get the array to start.

root@MythTV:/home/ken# mdadm --examine /dev/sdb4
/dev/sdb4:

     Raid Level : raid6
   Raid Devices : 7

     Array Size : 13165485120 (12555.59 GiB 13481.46 GB)
  Used Dev Size : 5266194048 (2511.12 GiB 2696.29 GB)

   Array State : AAAAAAA ('A' == active, '.' == missing, 'R' == replacing)

You say this is a five-disk RAID-6 array, but the disk metadata says,
in three different ways, that this is a seven-disk array.  Do you have
any idea what could be causing this discrepancy?

-- 
Mark