Compaq ProLiant 6400R Compaq Parallel Database Cluster Model PDC/05000 for Ora - Page 44

2-20 Compaq Parallel Database Cluster Model PDC/O5000 for Oracle8i and Windows 2000 Administrator Guide I/O Path Definitions for Redundant Fibre Channel Fabrics In a redundant Fibre Channel Fabric, devices are accessed by the operating system using conventional SCSI addressing terminology. An I/O path consists of the complete physical interconnections from a given host (node) to a specific RAID storageset in a shared storage subsystem. Each path is identified by a unique 4-bit value that contains the port number (host adapter), bus number, and the unit name's target ID and LUN. Each unit name's target ID and LUN values use the format "Dxxyy," where 'xx' is the target number (0-15) and 'yy' is the LUN (0-7). A target number of 0 is always dropped from the unit number designation (for example, the unit number D0 is understood to be LUN0 on target 0). A host (node) uses the unit name to specify the source or target for every I/O request it sends to an array controller. The unit name can identify a single physical disk drive unit or a storageset that contains several disk drives. The port number (HBA) is assigned by the Windows operating system. Except for the LUN, the rest of the SCSI address is created within the host adapter miniport driver and is determined by the actual connections between Fibre Channel SAN Switch ports and array controller ports. Controller ports connected to lower-numbered Fibre Channel SAN Switch ports are assigned lower SCSI bus and target ID values than those connected to higher-numbered switch ports. The LUN number is derived from the unit number that has been assigned to the storageset using the StorageWorks Command Console (SWCC) or Command Line Interface (CLI) commands. Each storageset created in a MA8000/EMA12000 Storage Subsystem must have a unique unit name. Since these storage subsystems present an identical address space from both of their two array controllers, the only bit of address information that will be different across the I/O paths from a given node to a specific storageset is the port (HBA) number. While cluster nodes use the unit number (Dxxyy) to identify and access a storageset or a single disk drive unit in the shared storage subsystems, the array controllers use a Port-Target-LUN (PTL) address to identify and access these resources in their storage subsystem. For the MA8000/EMA12000 Storage Subsystem, the PTL address contains the following information: I The SCSI port number (1-6) identifies the disk enclosure in which the target physical disk drive is located. I The target ID number (0-5 and 8-15) of the device identifies the physical disk drive. I The LUN of the device (For disk devices, the LUN is always 0.)