How NetBackup reserves drives
In multiple-initiator (multiple host bus adapter) environments, device-level access protection is required to avoid unintended sharing of tape devices and possible data loss problems. (Shared Storage Option is a multiple-initiator environment.) Access protection on a tape drive prevents an HBA that is not the reservation owner from issuing commands to control the drive. SCSI access protection operates at the SCSI target level and depends on correct operation of the fiber-to-SCSI bridge or the native fiber device hardware.
The only commonly available technique for this purpose is SPC-2 SCSI reserve and release functionality. All tape drive vendors support the SPC-2 SCSI reserve method. NetBackup has used SPC-2 SCSI reserve since NetBackup 3.4.3; it is the default tape drive reservation method in NetBackup. SPC-2 SCSI reserve is effective for most NetBackup environments.
Alternatively, the new SCSI persistent reserve method may be more effective in either of the following environments because it provides device status detection and correction:
NetBackup media servers are in a cluster environment
NetBackup can recover and use a reserved drive after a failover (if NetBackup owns the reservation). (With SPC-2 SCSI reserve, a drive reset usually is required because the reservation owner is inoperative.)
Environments where high drive availability is important
NetBackup can resolve NetBackup drive reservation conflicts and maintain high drive availability. (SPC-2 SCSI reserve provides no method for drive status detection.)
However, the SCSI persistent reserve method is not supported or not supported correctly by all device vendors. Therefore, analyze the environment to ensure that all of the hardware supports SCSI persistent reserve correctly.
NetBackup lets you configure either SCSI persistent reserve or SPC-2 SCSI reserve.
The following table describes the protection options.
Table: Protection options
You can configure access protection for each NetBackup media server. The protection setting configures tape drive access protection for all tape drive paths from the media server on which the setting is configured. The media server setting for any drive path can be overridden.
SCSI reservations provide protection for NetBackup Shared Storage Option environments or any other multiple-initiator environment in which drives are shared.