Disk sets must be created and configured using the Enhanced Storage command line interface (the metaset(1M) command). After you have created a diskset, you can administer state database replicas, volumes, and hot spare pools within a disk set using either Enhanced Storage Tool or the command line utilities.
After drives are added to a disk set, the disk set can be reserved (or taken) and released by hosts in the disk set. When a disk set is reserved by a host, the other host in the disk set cannot access the data on the drives in the diskset. To perform maintenance on a diskset, a host must be the owner of the disk set or have reserved the disk set. A host takes implicit ownership of the disk set by putting the first drives into the set.
The SCSI reserve command is issued to each drive in the disk set to reserve it for exclusive use by the current host. Each drive in the disk set is probed once every second to determine that it is still reserved.
Note - If a drive has been determined unexpectedly not to be reserved, the host will panic. This behavior helps to minimize data loss which would occur if two hosts were to simultaneously access the same drive.
Before a host can use drives in a disk set, the host must reserve the disk set. There are two methods of reserving a diskset:
Safely - When you safely reserve a disk set, Enhanced Storage checks to see if another host currently has the set reserved. If another host has the disk set reserved, your host will not be allowed to reserve the set.
Forcibly - When you forcibly reserve a disk set, Enhanced Storage 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 set are taken over and FailFast is enabled. The metadevice state database is read in on the host performing the reservation and the shared volumes configured in the 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 drives in a disk set are reserved by only one host at a time. A normal situation is defined as both hosts up and communicating with each other.
Sometimes it may be desirable to release a disk set. Releasing a disk set can be useful when performing maintenance on the drives in the set. When a disk set is released, it cannot be accessed by the host. If both hosts in a disk set release the set, neither host in the disk set can access the drives in the set.