Karl Paulsen / 04.03.2002
New Structures for Storage
Over the past decade, professional video server applications have weathered many changes -- especially in storage structure. Advances in storage architectures have shown a migration from JBOD (just-a-bunch-of-disks), through simple RAID arrays, and on to more complex and common storage systems. Now, for both media and data applications, moves toward storage networking are well under way.
With the new physical changes in storage architectures comes the management of that data, a natural expectation as both the quantities of storage and the needs of the organization continue to rise.
Storage management for the IT community has traveled a more difficult road than has the video server application. For IT, providing a single point of command and control has been taxing. For video server applications, the tasks are now beginning to surface in earnest.
How the correlation between increased storage requirements, third-party hardware (such as switches and fabrics), and the ever-growing complexities in handling mixed media formats - including low bit-rate proxies and high bit-rate transport stream technologies - are just some of the topics that will mold the next few years of media server deployment.
For the IT province, the mixture of topologies and technologies in storage has brought us some now rather common, but frequently misapplied, household words. These include SAN, NAS, Fibre Channel, TCP/IP and others. In addition, buzzwords such as scalability, manageability and compatibility are further intermixed with the concepts of backup, protection, redundancy and disaster recovery.
NAS VS. SAN
Comparisons between Network Attached Storage (NAS) and Storage Area Networks (SAN) still raise confusion in the networking community. This column will bring an update on both, plus provide some answers to questions of compatibility, scalability, management and deployment of SAN and NAS architectures.
The SAN is based on Fibre Channel, which provides a scalable, high-performance network storage architecture. Switches, directors and fiber-ready storage arrays allow both high performance (> 200 Mbps) and greater server extensibility than is possible with SCSI. Network Attached Storage (NAS) can also be readily scaled by adding capacity, up to multiple terabytes, or by adding multiple NAS appliances on the network.
Since NAS architectures can rely on existing TCP/IP networks, long-distance storage extension is possible. Developments in IP (i.e., FCIP and iSCSI) are adding to long-distance storage extensibility too.
Moving the SAN and NAS together is aimed at both consolidation and efficiencies for data-centric environments. A converged SAN/NAS solution makes use of Fibre Channel's abilities, allowing users to adapt storage resources to drive applications for greater scalability, distance and performance.
Consider that Storage Area Networks use a common storage pool, with Network Attached Storage acting in the role of a SAN that works at the file level and remotely mounts disk volumes from a server or appliance through protocols such as NFS or CIFS. Fibre Channel then becomes the medium, consisting of mesh or switch fabrics that interconnect the SAN.
Replication, backups, restores and security are key considerations in storage management in an enterprisewide network. Today, storage system features are broadly focused on scalability, management, availability and server consolidation. In the SAN, these concepts include the interconnection of storage systems, implementation of backup devices (including servers), and the reduction of LAN traffic aimed at improved network performance.
High availability - that is, the ability to respond to disaster recovery, live backup and failover support - is one of the principal concepts in the SAN architecture. NAS, on the other hand, provides the mature network topology - offering fast file access time and availability through data replication, employed with network appliances for a secure and protected file-level storage. Providers having Fibre Channel SAN and NAS can offer host servers multiple levels of storage connection, performance and availability - all from a single network infrastructure.
Certain prescribed parameters act as guidelines when considering SAN, NAS or a combination of the two. Interoperability, the often-overworked term for the better-understood word "compatibility," has improved over the past years; yet certain guidelines should still be followed.
One principal guideline suggests that implementation of a SAN fabric should include components from a common vendor's product family. Single sourcing narrows the choices in third-party hardware, but focuses compatibility issues to a more refined and controllable set of parameters.
There are those who believe the SAN and NAS system are competitive technologies, but in reality, they should be considered complementary.
By employing Fibre Channel switches and directors, NAS appliances or servers can be attached - permitting access to their storage volumes the same as any other server in the Fibre Channel network. Common disk-centric management and backup routines can then be applied to all storage, with NAS appliances being directly connected to the storage arrays.
Common storage management software, multiple file types and service classes are also possible with NAS; these are achieved by employing today's FC and tomorrow's FCIP and iSCSI technologies. Servers are still permitted to have a dual-access method, with Fibre Channel for some volumes and NFS-mounted drives for other data.
Advantages to NAS include accelerated response time, expansion in operations, reduction of I/O bottlenecks, increased availability and improved reliability. NAS is installed quickly and easily, is relatively inexpensive and eliminates storage islands.
For the SAN, storage growth scalability and manageability are key. Factors such as data replication and mirroring, higher availability of data and disk I/O improvements continue to move the IT community forward as they tackle the issues of recovering data center space through consolidation.
SAN is noted for disaster recovery capability as well as its ability to separate storage from data processing. By implementing server clustering and data replication, the storage network is further extended to a highly available, fault-tolerant system.
Network storage, whether applied in the IT or the video sense, is an emerging technology. With Fibre Channel viewed as the default protocol for most SAN design, NAS becomes a means to share files and cover long distances. The ability to bridge remote Fibre Channel SANs, using IP networks running at multiple, high gigabit rates, will allow the storage network to reach even greater distances. Harmonizing multiple protocols - such as Gigabit Ethernet and iSCSI - further extend the future proofing of storage, allowing a technology architecture to be molded to the applications needed most.