AIX supports I/O fencing with SCSI-3 Persistent Group Reservation (PGR) enabled.
chdev -l hdisk# -a reserve_policy=no_reserve
In this configuration, remote applications cannot accidentally create and remove registrations on disk.
chdev -l hdisk# -a reserve_policy=PR_shared
This PR_shared setting may allow any remote application (such as database devices) to open the disk that automatically creates and removes registrations on the device. This can make the database devices susceptible to data corruption.
The preferred method is raw SCSI-3 PGR API, however, some IBM storage devices like DS5800 do not support raw SCSI-3 PGR. For this reason, set the reserve_policy to no_reserve first. If the Adaptive Server instance fails to start due to I/O fencing issues, then the device does not support raw SCSI-3 PGR API. In such cases, the devices must be configured to use DKPRES API, in which case, set the reserve_policy to PR_shared.