IP storage: taking it to the next level

Computer Technology Review, April, 2004

Storage demands are growing at such a high rate that existing architectures like Fibre Channel SANs and Gigabit Ethernet NAS are already starting to reach their limitations. Fortunately, the new iSCSI protocol--which facilitates data transfers over intranets and manages storage over long distances--positions IP storage as the solution to these architectural limitations. For the enterprise, iSCSI is a natural for e-mail, database, and business continuance applications, as it mainly uses server-based replication software and takes advantage of the IP backbones and enterprise networks already in place with low-end and midrange servers.

The rise of iSCSI and IP storage coincides with the declining popularity of parallel interfaces, with their inherent physical limitations, and the increasing popularity of Serial ATA (SATA) and other inexpensive serial interfaces (disk drive vendors, in fact, are now delivering enterprise-level devices with SATA interfaces that provide 10,000 RPM, 1.2 million hours MTBF, 5.2 millisecond seek time, and five-year warranties, at prices 30% lower than traditional SCSI drives). It also coincides with the trend away from direct-attached storage; low-end devices are now coming on the market that will allow smaller enterprises to implement an IP storage network without having to add a dedicated support staff.

There are two types of iSCSI devices: initiator-side. The initiator side includes file servers, workstations and other host devices that exchange block data with target-side devices, such as tape libraries and disk arrays, over the IP network, using storage routers, switches and other types of networking equipment. Numerous initiator devices are available today to connect to the IP SAN, but there are very few of the target-side devices needed to take IP storage to the next level.

Target-Side Devices on Target

To provide an efficient, performance-oriented IP-based SAN solution, target-side devices must have TCP/IP and iSCSI off-load functionality, iSCSI header and data digest, cache management, VLAN zoning, Quality of Service, high-availability features such as redundant mirror channel at zero latency, and direct data placement capability. And in order to leverage the economic benefits of SATA, it also must overcome the limitations of SATA interfaces in terms of the number of drives that a chip component can address. A typical storage controller using two PCI-X chips with eight SATA-II ports--each connected to a disk drive--can support only 16 SATA drives, which hinders the cost-effective scaling up of SATA storage. To pool and provision more than 70 terabytes of data storage, a target-side device for the enterprise requires an architecture that can support the new SATA-II Port Expansion, external cabling capabilities allowing for connectivity to 240 SATA devices, and a comprehensive set of volume virtualization such as RAID, Online Capacity Expansion, volume migration, and Diskline protection.

One such device is a scalable 10-gigabit-per-second iSCSI storage server controller (soon to be released by iStor Networks) that's designed to meet networked storage requirements, both internal and external. The GigaStorATX Storage Server is a highly integrated storage controller solution designed to conform to the ATX form factor specifications. This allows OEMs, VARs, and System Integrators to use off-the-shelf PC Server and Storage chassis to build high-performance, feature-rich, cost-effective iSCSI RAID storage solutions. The GigaStorATX enables current NAS or file-based providers the opportunity to create block-based, cost-effective RAID storage solutions by integrating the controller into their existing packaging and deploying the industry's latest technology, iSCSI. Each controller would still have only 16 SATA-II channels per controller, but the architecture would allow for inexpensive SATA-II expansion. Having all these drives connected to a single command controller would spread out the cost of controllers for a better cost/capacity ratio, providing an affordable solution for primary storage, fixed-content storage, content-addressable storage, disk-to-disk backup, and other applications.

For the growing enterprise, this kind of architecture would also provide cost-effective entry-level solutions with scalability. The initial purchase might include a limited number of front-end iSCSI ports and back-end SATA-II connections. As needs arise, it would enable much higher-end solutions that deploy all eight 1-GbE iSCSI front ends for host performance and connectivity and use SATA-II expansion technology to increase the available devices and capacities as applications continue to grow. The architecture's dual-active configuration environment would feature two storage server controllers, each with up to eight 1-GbE ports or a single 10-GbE port on the front end. The back-end interface would be agnostic and support SATA, SATA-II, Serial Attached SCSI (SAS), or Fibre Channel allowing for new technologies but also the mainstay of the storage industry (Fibre Channel).