Partitioning Software: The iSNAP 2100 architecture splits its services into three areas: hardware, firmware, and software (Fig. 2). The hardware performs packet processing at wire speeds. Firmware is stored in flash memory. This software drives the on-chip state machines, the four specialized packet processing nodes, and the general-purpose processor.
Silverback Systems provides firm-ware to accomplish TCP/IP and iSCSI. But the firmware can be enhanced to add functionality or to support other protocols.
The host device driver software varies from a limited facade, where the iSNAP 2100 does most of the processing (such as basic TCP/IP support), to substantial features for more complex protocols like CFIS and NFS. In these cases, the firmware handles the protocol basics, while the device driver completes the protocol. The amount accomplished in each depends upon the particular implementation.
The host operating system and the target system may also affect how services are partitioned. For example, a storage device might be configured so that the iSNAP 2100 executes a majority of the action, while a blade server moves more of the support software into the device driver side.
Hardware Connections: The iSNAP 2100 connects to the network through two GE links that can operate in full-duplex mode. Other data outlets include the PCI-X interface and the SPI-3 interface.
Normally, the PCI-X interface is deployed on endpoint adapters, like a blade server or an NAS device to transfer packet data between the iSNAP 2100's main memory and the host's main memory. In this case, the SPI-3 interface is typically unused, because there wouldn't be a switch fabric on board. The DMA interface allows the iSNAP 2100 to move data across the PCI-X bus without additional host intervention. Additionally, the iSNAP 2100 can manage work completion queues in the host's main memory, thereby minimizing host interaction with the iSNAP 2100.
The SPI-3 interface connects an iSNAP 2100 to an OC-48 switch fabric like those found with a network switch. The iSNAP 2100 can be used to build the typical GE switch, but more likely it will be a storage-aware GE switch. Normally, a traffic manager will be part of the SPI-3 fabric interface to take care of advanced queuing and scheduling. The SPI-3 interface can handle in-band control, but the main control interface can still happen over the PCI-X bus. The PCI-X interface will still be used when the iSNAP 2100 is part of a network switch. This interface allows a host processor to handle higher-level protocols such as IPsec, a security protocol.
Typically, the iSNAP 2100 carries out operations like logical unit number (LUN) lookup using off-chip memory and the on-chip processors. It also is possible to add specialized devices like content addressable memory (CAM) via the flash memory interface to augment the processing power of the iSNAP 2100.
Internally, the iSNAP 2100 doesn't use interrupts when processing packets. Instead, it employs queues to control access to resources and data. The iSNAP 2100 can interrupt the host processor, although interrupts tend to be minimal because the iSNAP 2100 handles most data movement and queue up-dates on its own.
System Development Tools: The iSNAP 2100 has a JTAG interface for low-level debugging. There also is a management serial interface port that provides a less intrusive but more functional interface to the iSNAP 2100.
The iSNAP 2100 is available on an evaluation board. The PCI-X HBA form factor board contains an iSNAP 2100 along with 512 Mbytes of DDR-SDRAM, 32 Mbytes of SRAM, 2 Mbytes of flash memory, and two GE connections. There's a connector for the SPI-3 interface, and the board plugs into a PCI-X socket.
Plus, there's a software simulator. It has a software shim that emulates PCI transactions so that a device driver can access the simulator in the same fashion as it would access the hardware. The simulator runs on Solaris, and reference drivers are available for Linux. Overall, the available software and prototype hardware offers a good base for developing network storage-based solutions.
Distributed storage is quickly be-coming critical in enterprise networks. IP-based storage and protocols like iSCSI are now becoming common. But their overhead can bog down a host processor, making the iSNAP 2100 key to building an efficient network storage system.
If the success of Ethernet is any indication about the rate of adoption for IP-based storage solutions, then the iSNAP 2100 will find a home in quite a few products.
Price & Availability
The iSNAP 2100 costs under $150 in OEM quantities. The iSNAP 2100 evaluation board and software simulator are available immediately. Device drivers and iSNAP 2100 firmware are also available.
Silverback Systems Inc., 695 Campbell Technology Pkwy., Suite 150, Campbell, CA 95008; (408) 376-1300; www.silverbacksystems.com.