COMSTAR and iSCSI Technology (Overview)

iSCSI is an acronym for Internet SCSI (Small Computer System Interface), an Internet Protocol (IP)-based storage networking standard for linking data storage subsystems.

By carrying SCSI commands over IP networks, the iSCSI protocol enables you to access block devices from across the network as if they were connected to the local system. COMSTAR provides an easier way to manage these iSCSI target devices.

COMSTAR utilizes a SCSI Target Mode Framework (STMF) to manage target storage devices with the following components:

• Port providers (or plug-ins) — Implement protocols, such as Fibre Channel (FC) and iSCSI.

• Logical unit providers — Emulate various SCSI devices, such as disk and tape devices.

• The management library (libstmf) — Provides the COMSTAR management interface. The modules that implement the iSCSI functionality do not need to interact directly with the underlying transport. In a similar way, the modules that implement the transport protocol are unaware of the SCSI-level functionality that is inherent in the packets they are transporting. Some transport examples are Fibre Channel and iSCSI. The framework separates the execution and cleanup of SCSI commands and the associated resources. This separation simplifies the task of writing SCSI or transport modules.

  The administration commands include:

  stmfadm

  manages SCSI LUNs

  itadm

  manages iSCSI targets

If you want to use storage devices in your existing TCP/IP network, the following solutions are available:

• iSCSI block devices or tape – Translates SCSI commands and data from the block level into IP packets. Using iSCSI in your network is advantageous when you need to have block-level access between one system and the target device, such as a tape device or a database. Access to a block-level device is not locked so that you could have multiple users or systems accessing a block-level device such as an iSCSI target device.

• NFS – Transfers file data over IP. The advantage of using NFS in your network is that you can share file data across many systems. Access to file data is locked appropriately when many users are accessing data that is available in an NFS environment.

Here are the benefits of using Solaris iSCSI targets and initiators:

• The iSCSI protocol runs across existing Ethernet networks.

  • You can use any supported network interface card (NIC), Ethernet hub, or Ethernet switch.

  • One IP port can handle multiple iSCSI target devices.

  • You can use existing infrastructure and management tools for IP networks.

• You might have existing Fibre-Channel devices that can be connected to clients without the cost of Fibre-Channel HBAs. In addition, systems with dedicated arrays can now export replicated storage with ZFS or UFS file systems.

• There is no upper limit on the maximum number of configured iSCSI target devices.

• The protocol can be used to connect to Fibre Channel or iSCSI Storage Area Network (SAN) environments with the appropriate hardware.

Here are the current limitations or restrictions of using the Solaris iSCSI initiator software:

• Support for iSCSI devices that use SLP is not currently available.

• iSCSI targets cannot be configured as dump devices.

• Transferring large amounts of data over your existing network can have an impact on performance.

COMSTAR Software and Hardware Requirements

• Solaris storage software and devices

• The storage-server software package for the system that provides the storage devices

• Any supported NIC