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| Driving Down the Cost of SANs |
| Apr. 18, 2005 |
Hoping to help drive down the cost and complexity of storage area networks (SANs) and thereby entice more businesses into using them, Microsoft has launched a new logo program called "Simple SAN." SANs allow multiple servers to access external storage controllers, and they can provide higher availability, scalability, and efficiency than direct-attached storage (DAS). Microsoft also released Version 2 of the iSCSI driver software for Windows Server 2003, which makes building SANs with fully redundant networks less expensive. However, even though SANs are now less complex and their price is coming down, direct-attached storage has become so cheap that SAN vendors will still have a hard time finding a market for SANs in the small or mid-size business segments. SANs Not Just for Large Organizations? Microsoft's Simple SAN initiative is based on its analysis that significantly more medium-size and small organizations will use and benefit from SANs if their cost and complexity are reduced. What Are SANs? SANs enable servers to share one or more external disk storage arrays over a network using a protocol designed for transferring block-level disk data. Each storage device consists of a Fibre Channel or iSCSI network interface, a storage controller, and redundant striped or mirrored disk sets (i.e., RAID). Unlike network-attached storage (NAS) servers, which serve files to other computers using common network file-sharing protocols, such as the Network File System (NFS) or Microsoft's Server Message Block (SMB), these storage devices do not run a general purpose OS, such as Windows or Linux, but instead run a small hardware-specific OS tailored for their primary task of reading and writing block-level data to disk. (However, many higher-end NAS devices are actually built on top of a SAN.) The storage controllers carve up the physical storage into logical disk volumes and publish them to the SAN. They also control security such that each logical volume can be restricted to a designated server or can be shared or read by multiple designated servers or backup devices. Instead of each server having only its own exclusive direct-attached storage (DAS), servers connected to the SAN see all logical volumes for which they have either read-only or read-write access permissions. To the Windows OS, these logical volumes look and behave just like disk partitions on DAS drives. With the proper hardware support, a SAN-attached server can even boot off a SAN volume and write its paging file to it, allowing the server to run without any DAS at all. Benefits to Small and Mid-Size Businesses Some large organizations use SANs because they allow an organization to connect its PC servers to the same storage arrays and backup technology used by their mainframes, allowing the servers to glean the benefits of enterprise-class fault-tolerant storage at relatively low marginal cost. SANs can also provide a key component in replicating an organization's critical data to a remote disaster recovery site. However, these solutions are expensive, complex, and therefore tend to be limited to large companies. However, small and mid-size organizations could potentially benefit from other unique SAN capabilities, particularly the following: Dynamic storage expansion and reallocation. With DAS, when a volume needs to grow larger, it usually requires backing up the volume to tape, adding or replacing disk drives, reformatting the disks, and then restoring the data. This process is labor-intensive and takes the server out of service for an extended period. As a result, many organizations purchase much more storage than they anticipate ever needing, and since unused DAS cannot be used by other servers, each server has to have its own reserve storage. In contrast, most SAN technologies virtualize storage so that disk volumes can be expanded dynamically without disrupting file system access or the applications writing to the disk storage. This means that organizations can purchase additional disk storage when they need it, and because reserve storage can be allocated to any volume in the storage array, much less reserve storage is needed. Support for huge storage needs. Current servers with DAS simply cannot scale up to the multiple terabytes (TBs) of storage required for large databases, such as ones that contain graphical or multimedia data like video or MRI scans. The practical limit for current internal RAID5/SCSI-based storage arrays is about 1TB, while some SAN-based storage arrays can scale well beyond 50TB, with disk controllers designed for throughput commensurate with the huge volumes. Multiple storage access paths for backup and clustering. SANs make it possible for multiple servers to access the same stored data and can thereby help increase the availability of applications, especially database applications such as SQL Server and Exchange. SANs help in two ways. First, even though DAS storage volumes can be made fault-tolerant by using RAID technology, this does not mean that the applications using them are fault-tolerant or highly available. SANs, however, can support clustering schemes (such as in Microsoft's Cluster Service) that enable one server to take over disk access from another if the original server or the application running on it fails or is taken offline. Second, SANs support direct disk backup. With DAS, the only access path to stored data is via the server that owns it. This path becomes a bottleneck during backup as the server transfers all data from the disk to the network, which can heavily impact the performance of the applications running on it. When storage volumes grow into the TB range, this problem becomes especially troublesome. With SANs, in contrast, a backup server can back up separate data snapshots directly from the storage array without impacting live application or database servers. Microsoft's Simple SAN Program Windows Server 2003 has built-in SAN support and includes many storage-related improvements, including the following:
The Simple SAN program aims to further simplify SANs and drive down costs mainly by hiding the complexity and streamlining the steps necessary for successful setup. It accomplishes this by limiting the number of feature decisions organizations have to make, focusing only on features that are relevant to the needs of smaller businesses. The program does not involve any new Microsoft or third-party technology; it is basically a logo program designed to address three main goals: Ensure SAN interoperability with Windows Server 2003. By providing technical support and assistance for "Plugfest" interoperability testing to SAN hardware and software vendors, Microsoft helps assure that SANs carrying the Simple SAN logo are fully interoperable with Windows Server 2003. Simplified setup. By working with vendors to simplify setup processes and documentation of the individual SAN components, Microsoft hopes to reduce both the amount of configuration required and the potential for incorrect SAN configuration. Microsoft's goal is analogous to the way Plug-and-Play has made PC hardware installation and configuration easier. Provide SAN purchase guidance. By introducing the Simple SAN Logo Partner Program, Microsoft provides a way for customers to identify SAN hardware solutions that are simple and easily deployed. The following vendors, which include virtually all of the big names in the SAN industry, have announced support for the Simple SAN program: Brocade, Dell, EMC, Emulex, Engenio, EqualLogic, Hitachi Data Systems, Hewlett-Packard (HP), Lefthand Networks, Network Appliance, NSI, QLogic, StorageTek, Yosemite Technology, and Xiotech. SANs Still Pricey The cost of SANs has already dropped significantly due to increased competition and the maturation of iSCSI technology, which uses more common Ethernet-based cabling and switches to connect servers with storage arrays, rather than the more complex and costly Fibre Channel equipment. Still, based on the prices of current entry-level SAN offerings from Dell and HP, the starting price point for a 0.5TB SAN will be roughly US$15,000. In addition, because of the reasons for using a SAN in the first place, such as the need for higher availability and possibly clustering, the total cost will be substantially more when the costs of additional disks, backup servers, and redundant networks, adapters, controllers, and the Windows Server Enterprise Edition licenses (if clustering is required) are included. With 300GB (0.3TB) SCSI hard drives now available for about US$1,500 and RAID controllers going for about US$1,000, a fault-tolerant 600GB DAS array would cost roughly US$5,500, making the SAN storage substantially more expensive from the outset. In addition, even a Simple SAN will require higher installation costs and ongoing maintenance than DAS. Organizations can afford to overbuy DAS disk storage and still come out far ahead of SAN-based storage on a pure cost-per-MB basis. For this reason, only businesses that need storage features that DAS cannot provide will be likely candidates for Simple SANs. Resources More information on the Simple SAN initiative is published at www.microsoft.com/windowsserversystem/storage/simplesan.mspx. Additional iSCSI documents and the link to download the iSCSI initiator are available at www.microsoft.com/WindowsServer2003/technologies/storage/iscsi/default.mspx. Microsoft's earlier iSCSI support is described in "iSCSI to Simplify Windows Storage" on page 17 of the Apr. 2003 Update and in "Windows Networked Storage Enhanced" on page 13 of the June 2004 Update. Windows support for SANs and NAS is explained in "Windows .NET Server Supports Enterprise Storage" on page 3 of the Dec. 2002 Update. |
