Consolidate server storage and ease your management burden with NAS and SAN
The growth of the Internet and the increasing demand for digital information have caused storage needs to expand dramatically. Yet, the digital economy's demand for 24 x 7 access to information leaves little time even for routine maintenance—let alone disruptive and time-consuming processes such as adding storage.
The need for an efficient way to manage storage has spurred interest in both Network Attached Storage (NAS) and Storage Area Network (SAN) solutions. Collectively referred to as storage networking, both technologies promise to ease the management burden by consolidating server storage and letting administrators manage one homogeneous storage pool from a central location.
NAS and SAN
NAS systems are essentially specialized file servers whose OSs are customized for speedy file service. NAS systems connect to a LAN and provide data access at the file level. Many NAS systems support both the Common Internet File System (CIFS) and NFS protocols so that both Windows and UNIX clients can access the same files. NAS systems range from basic 40GB workgroup models, such as Quantum's Snap Server 1000 ($499 direct), to large, full-featured enterprise-level systems such as Network Appliance's NetApp F880c, which offers a capacity of as much as 12TB, two clustered dual-processor systems, Fibre Channel—based RAID arrays, and redundant hot-plug power supplies (F880c pricing starts at about $200,000). NAS systems are available from many vendors, including Compaq, EMC, Dell, Hewlett-Packard (HP), IBM, Procom Technology, Raidtec, RAIDZONE, and LSI Logic.
SAN storage is designed for applications such as database-management systems and online transaction processing (OLTP) programs, which demand high-volume, block-level disk access rather than file-level access. SANs consolidate data into shared storage arrays, removing the storage burden from your servers and linking the arrays, servers, and your backup tape libraries into a back-end network. SANs typically support a variety of OSs, so you can use UNIX servers along with Windows systems. However, each OS can access only those storage resources assigned to it. SANs typically are Fibre Channel based, and a Fibre Channel switching fabric or hubs tie the devices together. Consequently, you need to install Fibre Channel host bus adapters (HBAs) on each server on the SAN.
Like NAS systems, SANs are available from many vendors, including Nishan Systems, Compaq, Hitachi, Dell, IBM, EMC, XIOtech, HP, Brocade Communications Systems, Gadzoox Networks, McDATA, QLogic, Vixel, and SAN Valley Systems. SAN packages typically include Fibre Channel HBAs, Fibre Channel switches or hubs, SAN management software, and sometimes a bridge to interface SCSI devices to the Fibre Channel network. Some components, such as the HBAs, switches, or hubs, might be from third-party vendors, but the SAN vendor usually provides a single point of support.
Small SANs—those that support as many as 20 servers—might have a Fibre Channel—arbitrated loop hub and one storage array with a capacity of 1TB or 2TB. Midsized SANs might support as many as 40 servers, one or two Fibre Channel switches, and a storage array with a capacity of roughly 4TB to 7TB. Very large SANs could have several Fibre Channel directors (i.e., switches with high-availability features and many ports) and storage arrays and support several hundred servers. SANs are extremely expensive—a small one can cost a few hundred thousand dollars, and large ones can cost a million dollars or more.
Although both NAS and SAN solutions provide efficient storage management, NAS systems are easier to install and configure and generally are less expensive than SANs. Many enterprise-class NAS products provide better performance, scalability, and reliability than general-purpose file servers.
SANs provide outstanding scalability—you can easily add storage to arrays or attach new arrays to SAN hubs or switches. In addition, SANs move storage traffic off the LAN, improving application performance. This performance improvement is especially evident during a SAN's characteristic LAN-free backup, in which data moves directly from the storage arrays to the SAN-connected tape library without tying up LAN resources, as Figure 1 shows. SANs also offer outstanding reliability because you can construct the network with redundant paths, as Figure 2 shows, and can mirror data to several arrays to ensure data access should a disk or switch failure occur.
Interoperability
As I implied earlier, however, SANs are difficult to assemble and configure. A lack of interoperability between third-party Fibre Channel switches makes creating a switching fabric that uses products from multiple vendors difficult or impossible. Interoperability is also a problem between Fibre Channel HBAs and network-management frameworks that provide SAN management capabilities—a situation that limits your HBA choices to those that the software supports.
Interoperability concerns are probably the most significant hurdles facing the SAN market; however, that picture is slowly changing. Vendors are beginning to hammer out and support interoperability standards and certify their SAN management software on other vendors' hardware. The ANSI Fibre Channel Switch Fabric-2 standard defines a common Fibre Channel switch interoperability mode, which several vendors now support. In addition, the Storage Networking Industry Association (SNIA) recently developed a Fibre Channel HBA API, which lets network-management applications manage any compliant HBAs, and an Extended Copy command designed to let SAN storage-management applications initiate a LAN-free backup with other vendors' storage arrays. (For more information about SNIA initiatives, visit http://www.snia.org.)
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