We have 3x 3TB WD Red drives configured in a RAID 5 on an HP P812 controller with the latest firmware on.
However, drives keep being dropped randomly from the array upon reboots, though not always. It's always only one drive being dropped at a time and the problem doesn't seem to affect the WD Raptor, also connected to the P812. ACU reports that the affected drive is "missing or not connected properly" and the diagnostics simply reports that the drive is missing. Hot-reinserting the drive causes the controller to see the drive again, but requires a reboot to make the logical drive available again and so the cycle continues. All drives connect properly to the array in about 1 in every 5 reboots.
All 4 drives are connected to the internal port 5i using a Mini SAS SFF-8087 to 4 SATA fan out cable.
We tried this configuration in two different (non HP) environments but the same problem affected both.
We also tried the disks on a P800 and they worked fine there (although, given the P800 limitations, only 2TB of the disks were being recognised).
What could possibly be causing this problem?