Built a new MD stack yesterday comprising of 1x MD3200 and 2x MD1200, all populated with 3TB drives. Had the usual controller lockdown then recovery mode issues but easily fixed. All was well until I updated the MD3200 from 08.20.20.60 to the new 08.20.21.60 firmware.
Shortly after the update completed the MD3200 reported a unit ID conflict. Closer examination in the MDSM showed that both the MD1200's now had ID 48. ( Were previously 1 & 2, with the MD3200 being 0 )
Changed the MD1200's back to 1 & 2 and all seemed ok till they changed back to 48 a few seconds later!!!
Timed it and they ID's change to 48 after 20 seconds no matter what I did. Did a full power down and cold boot, changed the ID's through a SMCLI script, tried different MD1200's. In the end I dropped the MD3200 firmware back to 08.20.20.60 which resolved the issue.
All drives and the MD1200's were also running the latest firmware. I can only summise that there is a problem with the 08.20.21.60 firmware
I have the same problem on MD3600f with firmware 08.20.21.60. I have a case on Dell support. After downgrade to 08.20.20.60, it works