It's a 2-way street in iSCSI land. In a previous article we saw how the iSCSI protocol requires servers to have HBAs fitted with TCP/IP offload engines (TOEs) to relieve the server CPU from the TCP/IP work needed. The same is true at the other end of the link. Either a switch has to do the TCP/IP work and send/receive raw SCSI data from connected storage devices or convert between iSCSI and Fibre Channel (FC) to send the commands over a Fibre Channel fabric to storage devices which extract the SCSI commands from the FC frames and deal with the request.

What products are available to connect disk and tape devices to an iSCSI network and enable SCSI-accessed storage over the LAN or WAN?

Nishan and Cisco produce iSCSI switches which interconnect iSCSI networks to Fibre Channel ones and thus extend the reach of a Fibre Channel SAN. Neither company is positioning these as part of a raw IP SAN-only solution, nor as a SAN on a LAN solution. Existing FC SAN customers may well be excited by the idea of extending SAN use over IP networks rather than more expensive Fibre Channel.

Virtual adapters
Spectra Logic has announced the world's first iSCSI tape libraries and tape drives. It's NAStape is an iSCSI tape drive which can stream an LTO or Super AIT tape drive over Ethernet. Inside its Taos architecture, Spectra Logic has equipped its libraries with an Interface Controller which performs TCP/IP functions. It has protocol blades, one of which is for iSCSI. The connected servers can run a 'virtual adapter' which 'IP packetises' SCSI commands and sends them off to the IP address of the tape device with the controller. Servers run Veritas BackupExec or other standard backup package just as if the tape device was local to them. With multiple protocol blades a Spectra Logic library can be shared across different networks. Bill Reed, SVP sales and marketing for the company, explains: "Adding iSCSI to our existing NDMP and Fibre Channel library options offers Spectra Logic customers complete flexibility in storage networking, including the option to backup to a single library over both a LAN and SAN."

Overland Storage has acquired Okapi Software which has introduced iSCSI disk appliances. The ipXpress appliance enables low-cost ATA, and also Serial ATA, drives to connect over iSCSI to servers on the LAN. It is a way of sharing disk arrays between servers for small and medium enterprises, for providing block-level access to disks over the LAN and thus enabling basic SAN functionality. (NAS provides file level access to disks over a LAN). Also its backup accelerator takes backed up data off a shared disk and onto tape.

Disk-to-Disk-to-Tape
Overland's intention is to supply intelligent disk-based storage alongside its existing tape library and storage software management product lines. A particular aim is disk-to-disk backup, according to president and CEO Christopher Calisi; "We believe the Okapi backup accelerator appliance is the ideal solution. It uses two of the most promising new technologies, iSCSI and Serial ATA drives, to produce a very affordable appliance that facilitates 'Disk-to-Disk-to-Tape' or D2D2T backup (and) accelerates backup by up to eight times."

StorageTek has introduced its iSCSI-accessed EchoView disk array providing continuous backup of primary disks. EchoView is a dedicated data security device and not seen as part of a SAN infrastructure.

LSI Logic has demonstrated an iSCSI RAID controller using its MegaRAID technology connected to an IP SAN. The TCP/IP processing is carried out by an Intel IOP321 I/O processor. Phil Bullinger, VP and GM of LSI Logic's RAID storage adapters division, asserts that, "The lack of a simple, intelligent iSCSI RAID target solution has created a gap and delayed the deployment of IP SANs."

A shared tape device is a simple idea to take on board. A shared disk array, SAN style, is a different thing since the disk storage has to be apportioned out to servers and LUN concepts taken on board. The iSCSI (IP) SAN learning curve could be steep.

Users new to SANs may find the storage consolidation ideas and administrative overhead a balking factor when considering IP SANs. If they already have a datacentre then it won't be such a significant step. If they don't then it will represent a much bigger change in thinking. Performance will be a strong factor and we will look at that issue in the next and final iSCSI article.