Storage Area Networks (SANs) are gaining acceptance at an astounding rate as a solution for organizations that are experiencing explosive storage growth. A SAN consolidates your storage for easier storage management and better use of storage resources. A SAN will allow for scalability as you add more hosts and more storage and minimizes the downtime associated with those activities compared with a Direct Attached Storage (DAS) environment. A SAN environment can increase backup performance by offloading traffic from your IP network and freeing your host's processor from packaging the backup data for IP transmission. You can also take advantage of a SAN's any-to-any connectivity to implement redundancy and disaster tolerance both locally and across long distances.
Because SANs are similar to other network technologies you've probably worked with, you can draw some comparisons to bring yourself up to speed on SAN components and how they operate together. The various pieces fall into three categories: interconnecting devices, storage devices, and hosts. Interconnecting devices include hubs, switches, bridges, and routers. Storage devices range from Just a Bunch of Disks (JBOD) to highly redundant and intelligent RAID enclosures that scale to meet the needs of the largest enterprises. Hosts are the computers that attach to the SAN through a host bus adapter (HBA), which is akin to a NIC in a typical data network.
Deploying Fibre Channel switches in a SAN offers the same performance and manageability benefits as deploying switches in an Ethernet environment. Fibre Channel bridges and routers perform functions similar to their data-networking counterparts, enabling Fibre Channel connectivity to SCSI, Asynchronous Transfer Mode (ATM), and even Ethernet across long distances.
A wide range of SAN storage choices are available to fit different applications. On the low end, JBODs provide the most raw storage for the least amount of money. You can use native or third-party volume-management tools to implement software RAID on the disks in the JBOD enclosure, but Fibre Channel RAID enclosures offer more robust solutions along with better availability and manageability. Typical RAID enclosures include redundant core components and built-in management facilities.
Each host uses an HBA to connect to the storage devices in a SAN. Technically, legacy SCSI controllers are HBAs that connect the host to a SCSI device; HBAs on a SAN perform the same service in letting a host attach to Fibre Channel devices. HBAs process block-level I/O without relying on the host's CPU, thus minimizing the CPU and bus utilization I/O burden on the host. You can install multiple HBAs in a host to achieve redundant data paths and improve availability. In this Lab feature, I look at some SAN components and implement them as a fictional company, Datahogs, to show how a SAN can benefit your organization.
Datahogs SAN, Phase 1
Datahogs is a midsized, rapidly growing company that has several core Windows 2000 and Windows NT servers and a Sun Microsystems server running Solaris. During the past year, the IT staff has performed at least one storage upgrade on each server, and the Windows systems have nearly consumed the upgraded storage. In addition to the hassle of another storage upgrade, the backup administrator says that the company's current data has outgrown the time window available for backup operations, and another storage upgrade will only make the problem worse. Datahogs decides that investing in SAN technology will alleviate some of the company's headaches and provide a quick Return on Investment (ROI).
The company decides to use QLogic's SAN Connectivity Kit 1000, a relatively inexpensive kit that will let IT build a SAN from scratch. To maintain the company's recent investment in legacy SCSI storage and bolster the effectiveness of its existing SCSI tape library, the company will use ADIC's ADIC Gateway; to increase the speed, capacity, and availability of storage for the core servers, the company decided to purchase Dot Hill Systems' SANnet 7124 RAID enclosure.