Storage needs piling up

Communications News, April, 1998 by Morris Edwards

Vendors are finding ways to increase storage capacities while speeding access and data transfer and providing better management.

Network storage may not be a sexy subject, but for today's IT managers it's a critical. Storages is already the biggest line item in IT budgets, according to San Jose, Calif.-based research firm Dataquest, accounting for 35% of hardware purchases. Three years ago the figure was 30%.

What's more, storage needs are expected to soar over the next few years. Server storage, for example, is projected to grow at an annual compound rate of 91%.

Even in the face of this storage explosion, though, IT managers are under pressure to provide users with quick, reliable, and secure access to mission-critical data that is often scattered among many different platforms.

Fortunately, vendors are finding ways to increase storage capacities while speeding access and data transfer and providing better management. The advances are coming mainly from improvements in the workhorse RAID systems and from new concepts and technology such as Fibre Channel, storage area networks, and network-attached storage servers.

RAID BOOSTER

Where reliable access to data is critical to a firm's well-being, the most common storage solution is RAID, named for its configuration of a redundant array of inexpensive (or, some say, independent) disks. The idea was to aggregate a number of small hard drives to provide the capacity of a single, large drive at less cost and with greater fault tolerance. RAID also allows you to add disk volume without having to bring the server down, saving the backup and restore processes required for a single drive.

Recent designs have increased fault tolerance even further and boosted capacities and performance. Several of the drives can be accessed simultaneously to increase throughput. Also, the same disk space can be shared among multiple systems.

Performance can be further boosted by replacing the conventional SCSI (small computer systems interface) connection to the host with a Fibre Channel controller. Whereas the fastest SCSI channel operates at 40 Mbps and supports only 14 devices on a bus, Fibre Channel speeds can top 100 Mbps and up to 127 devices can be daisychained together to create large-capacity arrays.

Fibre Channel also has a significantly smaller footprint and overcomes SCSI's distance limitation of 25 meters. With single-mode fiber, Fibre Channel offers a range of 10 kin, or about six miles; with copper cabling the limit is 47 meters.

For the moment, Fibre Channel is more expensive than SCSI, but users who need high throughput or long-distance connections are willing to pay extra. Fibre Channel can also be used for the drives themselves, but this application is less attractive since the drives are physically limited to much lower speeds than the connection can support.

Most RAID suppliers offer Fibre Channel connections, and more than 150 companies are reportedly developing Fibre Channel products. Currently, Fibre Channel accounts for a tiny slice of the $16 billion RAID market, but that is about to change. Analysts expect the Fibre Channel market will grow at an annual compound rate of 60% through the year 2000, reaching $7 billion including hubs, switches, and adapters.

Sun Microsystems has entered the fray with a second-generation Fibre Channel offering, the A5000, which uses software-based RAID residing on the host, eliminating the cost of RAID controllers. Using a hub, four of the systems can be connected to multiple hosts.

STORAGE AREA NETWORKS

Fibre Channel Arbitrated Loop (FC-AL), the full name, is a serial transmission technology which requires only two conductors for a single connection, compared with a 68-wire cable for a "wide" SCSI connection.

It can move data at 100 Mbps in half-duplex mode or 200 Mbps in a full-duplex configuration. With its dual loop capabilities, Fibre Channel also offers fault tolerance. If one loop fails, you can still operate through the second one.

As an interconnection and communications technology, Fibre Channel can be configured in a point-to-point or switched topology for high-speed data transfer of large amounts of data among numerous devices.

This capability is put to use in storage area network--specialized switched networks that link multiple servers with a pool of storage systems. Storage area networks make data from any disk array accessible to any server at speeds of 100 Mbps and above.

To ensure that servers and storage systems from different vendors will be able to communicate with one another, major storage vendors have formed the Storage Networking Industry Association to develop standards and promote the new technologies. Vendors are also starting to develop the switches needed to move data between the servers and storage arrays.

IBM offers an alternative to Fibre Channel, known as Serial Storage Architecture (SSA), which it claims is less complex and costly. However, at 80 Mbps, its throughput is also substantially less. IBM points out that, with SSA, lots of drives can communicate with the bus at the same time, so the effective throughput can be greater.