HDK Technical Reference

SCSI multiple channels

HBA drivers written for SDI version 2 and later can support multiple SCSI channels.

The implementation includes support for multiple initiators, when two or more HBAs and SCSI-2 compliant disks on the same SCSI bus. In a high availability cluster, multiple initiators may be used in a single system to provide redundant I/O paths, or may be used across multiple systems to provide access to shared data and devices.

Multiple initiator features include error recovery for timeouts, bus resets, device busy, and reservation conflicts. Usually there is a layer above SDI that controls access to devices below in a multiple initiator system. In many cases, notification to this layer of a condition is the only required action to be taken by SDI.

In general, the multiple initiator support is encapsulated within SDI. Use of a bus reset by HBA drivers should only be done as a last resort. HBA drivers should call the sdi_xaen(D3sdi) function when a reset is detected on the SCSI bus and there are no outstanding jobs in the queue. Any outstanding jobs at the time of the reset should be failed with a completion code indicating that the failure was due to a reset on the bus.

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OpenServer 6 and UnixWare (SVR5) HDK - June 2005