Method and apparatus for implementing distributed SCSI devices using enhanced adapter reservations

DETAILED DESCRIPTION Principal aspects of the present invention are to provide a method and apparatus for implementing distributed (SCSI) devices using enhanced adapter reservations.
Other important aspects of the present invention are to provide such method and apparatus for implementing distributed (SCSI) devices using enhanced adapter reservations substantially without negative effect and that overcome many of the disadvantages of prior art arrangements.
In brief, a method and apparatus are provided for implementing distributed (SCSI) devices using enhanced adapter reservations.
A plurality of adapter is provided.
Each adapter implements a plurality of logical devices with each logical device respectively coupled to a port of the distributed SCSI devices.
The adapters manage reservations for the plurality of logical devices selectively using a no reservation state, an implicit reservation state, and an explicit reservation state.
The adapters assign one adapter for managing each of the plurality of logical devices.
In accordance with features of the invention, the adapters arbitrarily assign the resources to one of the adapters in the absence of a host reservation.
For example, the adapter that accesses a resource first gains access to the resource and is given an implicit reservation.
When an adapter has an implicit reservation, other adapters are blocked from using the resource and operations fail with a conventional reservation conflict response.
A host device driver is able to move resources between adapters using predefined SCSI reservation management commands.
In accordance with features of the invention, the adapters provide redundancy such that the resources can still be accessed even in the event of hardware failure.
The adapters are decoupled and are allowed to independently power up and power down.