Fail all the devices, then remove them, then stop the raid. eg
mdadm –manage /dev/mdfoo –fail /dev/sdfoo
mdadm –manage /dev/mdfoo –remove /dev/sdfoo
mdadm –manage –stop /dev/mdfoo
mdadm –zero-superblock /dev/mdfoo
viamdadm delete linux raid – Linux/BSD.