HP-UX iSCSI Software Initiator Support Guide (Edition 7)

7 The iSCSI Software Interface Driver
This chapter contains information on:
• “iSCSI Software Interface Driver Overview” (page 36)
• “iSCSI Software Interface Driver Technical Overview” (page 36)
• “System Startup” (page 36)
• “iSCSI Software Interface Driver Technical Specifications” (page 37)
• “Features” (page 37)
• “Limitations” (page 37)
• “iSCSI Software Interface Driver Configuration” (page 37)
• “Kernel Build” (page 37)
• “iSCSI Software Interface Driver Management” (page 37)
• “iSCSI Software Interface Driver Statistics” (page 38)
• “iSCSI Software Interface Driver Diagnostic Messages” (page 38)
• “iSCSI Software Interface Driver Daemons” (page 38)
• “iSCSI Software Interface Driver Daemon (iswd)” (page 38)
7.1 iSCSI Software Interface Driver Overview
The HP-UX iSCSI Software Interface Driver (SWD) is a host based implementation of the iSCSI
protocol that uses standard Network Interface Cards (NICs). There are no special network
infrastructure requirements.
The iSCSI SWD interfaces with the iSCSI transport layer for session management and SCSI support.
It also interfaces with the network stack above the TCP layer. iSCSI Protocol Data Units (PDUs) are
sent and received by the iSCSI SWD on the TCP stream.
The iSCSI SWD receives SCSI commands and data from the iSCSI transport layer and sends SCSI
responses to the iSCSI transport layer.
7.2 iSCSI Software Interface Driver Technical Overview
7.2.1 System Startup
In the standard HP-UX system startup sequence, access to mass storage is established before
networking is initialized. This order of events is in conflict with the iSCSI SWD, because iSCSI
target devices cannot be accessed prior to networking initialization.
When the iSCSI SWD attempts to:
— discover iSCSI targets
— activate volume groups with physical volumes on iSCSI targets
— access file systems on iSCSI targets
before network initialization is completed, the ENXIO errno is returned to the caller. This would
result in error messages being emitted from Logical Volume Manager (LVM) and some of the file
system specific commands.
Once the network is initialized, the iSCSI Software Initiator startup script performs iSCSI device
discovery and iSCSI target access operations (which failed before network initialization).
The resolution of the ordering problems described above has placed limitations on the iSCSI SWD.
Because network initialization is performed using the /var directory, the /var directory cannot be
36 The iSCSI Software Interface Driver