You can halt the system and then use the show-volumes command at the OpenBoot prompt to determine if a drive has failed.
For example:
ok select /pci@300/pci@1/pci@0/pci@e/scsi@0
See Prepare to Create a RAID Hardware Volume (FCode-based RAID Utility) for more information.
In the following example, the secondary disk in a RAID 1 volume is offline.
ok show-volumes Volume 0 Target 389 Type RAID1 (Mirroring) Name raid1test WWID 04eec3557b137f31 Degraded Enabled 2 Members 2048 Blocks, 1048 KB Disk 1 Primary Optimal Target c HITACHI H101414SCSUN146G SA25 Disk 0 Secondary Offline Out Of Sync Target 0 HITACHI
ok unselect-dev