SAN And NAS Meet In The middle ... Over Backup.

Although usually pitted as opponents, Storage Area Networks (SANs) and Network Attached Storage (NAS) are actually complementary technologies that are having an ever-increasing influence on today's corporate data centers. To fully take advantage of NAS and SAN, it is crucial that they work together to solve critical storage and backup problems--a development that has just begun to emerge.

A Quick Look At HAS

NAS storage solutions attach directly to the LAN and utilize a small, fast operating system to allow network users access to the data. Disk-based NAS devices such as Network Appliance Filers, simplify many time-consuming system administration tasks. Although it is traditionally seen as a disk storage technology, NAS implementations can also be found for other storage mediums, as well (CD, DVD, and tape).

The industry's leading provider of NAS hardware is Network Appliance, who now owns 60.1% of the market share, according to Pu Xiang, senior analyst of Dataquest. NAS' advantages over traditional captive storage are expected to fuel the growth of its annual revenue from $870 million in 1999 to over $8.3 billion in 2004.

The primary benefits of NAS are simplicity, scalability, and the ability to centralize the management tasks associated with storage. One feature that assists with manageability is that NAS protocols allow access to heterogeneous data types, including Windows and Unix. Simplicity is an issue because, as system administrators are being burdened with more data each year, more sys admins need to be hired or data manageability needs to become easier. Thus, NAS allows greater scalability from the management perspective. In addition to simplified management, the act of adding another NAS device is much less painful than with the traditional Direct Attached Storage (DAS), which is attached to a server. New devices can be quickly added as needed to keep up with data growth. In DAS models, each added system requires more initial effort, as well, as more ongoing operating system maintenance.

In certain markets where high performance file serving is important, NAS products such as those from Network Appliance offer improved performance over DAS architectures. Environments such as those with large CAD files and complex IC designs often see performance increases when using NAS and often perform significantly faster than when using a locally attached hard drive.

The cost of low-end NAS products can be comparable to adding more local disk space to a server at approximately $50 per gigabyte. High performance, high-end NAS products range upwards of $215 per gigabyte. This cost can often be justified by the performance gain it yields, as well as its ability to recover more quickly from a failure than server dependent storage.

Most NAS products utilize Fibre Channel disk drives within their enclosures. The Fibre Channel connects the disk arrays to the NAS system. This integrated NAS hardware, then, presents the storage to users via the LAN. The internal architecture allows high bandwidth connectivity, cabling simplicity, and higher device counts than SCSI connectivity methods.

Storage Area Networking Expands The Limits Of SCSI Topologies

The advent of Fibre Channel has brought about a new storage topology called Storage Area Network (SAN). Picking up as a logical extension to the SCSI interface, Fibre Channel SANs open many doors such as the ability to share storage resources between servers, increased bandwidth, and the ability to connect many more devices. Using a Fibre Channel SAN, devices can be located up to ten kilometers apart utilizing a healthy bandwidth of 100MB/sec.

SANs allow devices to be shared amongst multiple operating systems and servers. The challenge SANs have faced is overcoming existing storage architectures. Device drivers, software applications, and other key workings have been designed for traditional DAS architectures where the servers expect all storage and peripherals to be "captive" to themselves. As the architecture is opened up to allow sharing of these devices, architectural changes must be made to these key components to allow shared peripherals.

NM Backup Strategies

NAS and SAN architectures face different challenges as backup and data protection is brought into the equation. On one hand, NAS devices offer many advantages over DAS architectures, but on the other, the ultimate success of NAS may be restricted by its software limitations surrounding backup. While many NAS devices utilize Fibre Channel within the box, the operating system intelligence and system horsepower needed to effectively perform backup functions over a Fibre Channel SAN have not evolved to the same level of traditional DAS-based host systems.

Until recently, there have been three methods used to backup NAS devices: direct attached tape drives, direct attached tape libraries, and network backup. All three solutions solved the backup problem, but each led to its own difficulties. First, direct attached tape drives become expensive and cumbersome to manage. The risk of a human error and the increased cost of managing multiple tape rotations quickly make this option unattractive. Second, directly attaching tape libraries to each NAS device could help avoid the labor costs and human errors, but for most companies, it proved to be prohibitively expensive. Third, backing up NAS over the LAN through a LAN-attached storage server offers centralized control and the sharing of a tape library. However, it often created network bottlenecks, negatively affecting backup performance and user access to the NAS devices.

Backup In Multiple Network Appliance Filer Environments

The success of Network Appliance and its Filer products has finally exposed the NAS architecture's backup limitations. Utilizing the SAN back-end on the NetApp Filers, several leading storage industry vendors (Network Appliance, Spectra Logic, Vixel, Veritas Software, Legato Systems, and ATL/Quantum) recently collaborated to provide a method of sharing backup resources without the LAN-based backup limitations. The resulting SAN-based backup architecture offers users the best of both technologies: the NAS advantages of scalability and simplicity and the sharability of the SAN architecture. The solution allows one or more tape libraries to be shared between multiple Network Appliance Filers. As the customer's Filer base grows, more tape resources can easily be added to meet the increased backup requirements.

While this solution is the first instance of a multi-vendor effort ending in a hybrid SAN/NAS solution, users can expect to see this more often in the future. The scope of today's data growth is beginning to shift the challenges of just storing the data to include data protection, as well. This is causing the lines between storage vendors to become blurred as they work more closely to solve the data storage and protection problem together. 100% data access, 100% uptime, and unlimited scalability are the expectations of users. As in the past, technology will catch up.

Jonathan Sackheim is the channel marketing manager at Spectra Logic Corporation (Boulder CO).