Using Centos 6, how to I prevent mdadm from assembling arrays from specific block devices at boot?
Background: Due to an accident, one of my servers went down and on reboot, got stuck first at NFS statd, then at automount after I disable NFS in single user mode. Only after disabling autofs was the server able to complete booting into runlevel 3.
On investigation, it seems that mdadm added two new raid devices md126 and md127 assembled into read-only in degraded raid 1 mode from two unknown device dm-20 and dm-8. My guess is that automount was trying to mount these devices which caused the boot process to fail.
After doing some googling, I found the lsblk command and was able to identify dm-20 and dm-8 to be RAID devices created from two lvm logical volumes. These were added to virtual guests as raid devices using whole drives instead of partitioned raid.
Unfortunately, I had been unable to find out if it was possible to tell mdadm not to include these drives, the mdadm.conf manpage doesn't appear to list any such option. Is there some way to achieve this or is permanently disabling autofs my only option?