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Does ONTAP use SCSI Persistent Reservations?

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Applies to

ONTAP 9

Answer

SCSI reservations are used by NetApp storage systems for several reasons:
  • In a SAN environment, the NetApp fabric-attached storage system will set and honor classic release/reserve and persistent reservations for LUNs requested by initiators.
  • In a tape backup environment, the storage system can be configured to use SCSI reservations to reserve tape drives in a Dynamic Drive Sharing environment. 
    • In Data ONTAP releases prior to 7.1.1, SCSI reserve/release reservations were controlled by the options tape.persistent_reservations [on | off] command. 
    • Data ONTAP 7.1.1 and later added the ability to set either SCSI reserve/release or SCSI Persistent Reservations. The options tape.persistent_reservations command was deprecated and replaced with the options tape.reservations [scsi | persistent] command. 
  • NetApp High Availability (HA) storage controllers use SCSI reservations to control disk access.
    • For HA pairs using hardware disk ownership, SCSI reservations are only used during cf takeover.  
    • For HA pairs using software disk ownership, SCSI reservations are used regardless of whether the system is in cf takeover.
  • They are not persistent across power cycles of the disk shelves. Because of this, the node that has taken over will reassert the reservation at regular intervals in case the disk shelves lose power or a drive is reset.
  • While it is possible to see that a reservation exists, it is not possible to determine which node set the reservation.
  • Active-active cluster partners using SANOWN (Software Disk Ownership) use SCSI-3 Persistent Reservations to control disk ownership.
  • The reservations are used regardless of whether the HA pair is in cf takeover. These reservations are persistent across reboots.
  • The node owning the reservation has complete control over the disk, including read and write capabilities.
  • The SCSI-3 Persistent Reservations are reasserted every 30 seconds. 

Additional Information

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