COMSTAR: Common Multiprotocol SCSI Target

Introduction to COMSTAR

COMSTAR is a software framework that enables you to turn any OpenSolaris host into a SCSI target that can be accessed over the network by initiator hosts. COMSTAR breaks down the huge task of handling a SCSI target subsystem into independent functional modules. These modules are then glued together by the SCSI Target Mode Framework (STMF).

In following illustration, the OpenSolaris target host is configured as a storage array using COMSTAR. The initiator hosts can be any platform: Solaris 10, Windows, Linux, VMware ESX, etc.

The modules implementing functionality at SCSI level (disk, tape, etc.) do not need to interact directly with the underlying transport. Likewise, the modules implementing the transport protocol (Fibre Channel, iSCSI etc.) are not aware of the SCSI level functionality inherent in the packets they are transporting. The framework compartmentalizes the execution and cleanup of SCSI commands and the associated resources. This simplifies the task of writing SCSI or transport modules.

COMSTAR features include:

• Extensive LUN Masking and mapping functions
• Multipathing across different transport protocols
• Multiple parallel transfers per SCSI command
• Scalable design
• Compatible with generic HBAs

The port providers implement target transports, such as Fibre Channel. The logical unit (LU) providers implement SCSI logical units, such as disk, tape, and the like.

How to Get COMSTAR

COMSTAR is integrated into the latest Solaris Express Community Edition (SXCE) starting with SXCE build 90. You can get the latest SXCE from the OpenSolaris web site downloads page. COMSTAR is available by default after you install the latest SXCE (end user support or higher metacluster).

COMSTAR is also available in the OpenSolaris distribution starting with the 2009.06 release. As a convenience, you can install all the appropriate IPS packages by pkg install storage-server.

Related Projects

• iSCSI Extensions for Remote DMA (iSER) will provide iSCSI support for COMSTAR
• Fibre Channel over Ethernet will provide FCoE support under COMSTAR
• SRPT provides SRP Target support under COMSTAR