Overview
iSCSI reservations provide a mechanism to control how multiple initiators access a shared LUN. By placing a reservation, an initiator effectively locks the LUN, preventing other initiators from modifying it simultaneously. iSCSI reservations come in two primary forms: SCSI-2 “classic” reservations and SCSI-3 “persistent” reservations.
Classic Reservations (SCSI-2)
Classic (or SCSI-2) reservations can be released under two circumstances:
- When the initiator explicitly releases the reservation
- When a bus reset occurs as part of error recovery
This approach serves many legacy systems but can be limited by resets that automatically break the reservation.
Persistent Reservations (SCSI-3)
Persistent (or SCSI-3) reservations remain active until explicitly released by the initiator. Unlike classic reservations, persistent reservations are not dissolved by a bus reset, providing a more robust, modern approach to managing concurrent access in shared-storage environments.
Additional Notes
Persistent reservations are preferred in most current deployments to avoid unintentional release events. They offer greater control and resilience for cluster-aware applications that rely on shared disks without risking inadvertent interruptions.