Before a host can use the disks in a disk set, the host must reserve the disk set. There are two methods of reserving a disk set:
Safely - When you safely reserve a disk set, Solaris Volume Manager attempts to take the disk set, and the other host attempts to release the disk set. The release (and therefore the reservation) might fail.
Forcibly - When you forcibly reserve a disk set, Solaris Volume Manager reserves the disk set whether or not another host currently has the set reserved. This method is generally used when a host in the disk set is down or not communicating. All disks within the disk set are taken over. The state database is read in on the host performing the reservation and the shared volumes configured in the disk set become accessible. If the other host had the disk set reserved at this point, it would panic due to reservation loss.
Normally, two hosts in a disk set cooperate with each other to ensure that the disks in a disk set are reserved by only one host at a time. A normal situation is defined as both hosts being up and communicating with each other.
If a disk has been determined unexpectedly not to be reserved (perhaps because another host using the disk set forcibly took the disk), the host will panic. This behavior helps to minimize data loss which would occur if two hosts were to simultaneously access the same disk.
For more information about taking or reserving a disk set, see How to Take a Disk Set.