Design Considerations In Enterprise Storage Networks.

Marrying Storage Area Networks, Network Attached Storage and enterprise storage

The first part of this article appeared in the October issue (Q3 2000) of Storage Inc.

Business continuity means being able to minimize both planned and unplanned downtime (inaccessibility). This becomes more and more critical as NAS is both centralized and consolidated where a single outage could impact a large percentage of the organization. Unplanned downtime is typically addressed by eliminating single points of failure in the network, storage, and file server. It is beyond the scope of this article to address IP network design.

Enterprise storage systems (unlike JBOD systems) have built in redundancy. At the disk level, this is typically done through mirroring or RAID implementations. While any of these schemes eliminates single points of failure, consideration should be given to RAID group size as it directly impacts rebuild times while recovering from a failure--thus extending the exposure to a second failure leading to data loss. File servers typically utilize a combination of cluster capability (for high availability) and remote mirroring (ideally synchronous--for fault tolerance). Unplanned downtime is primarily due to data backup and maintenance. In order to avoid backup and maintenance from impacting operations, separate backup systems (file servers and disk) must be incorporated to perform that function. Typical implementations have a dedicated backup file server that mounts copies of the "live" file systems in order to perform zero-impact backups during operations.

Performance and load balancing capabilities of the NAS infrastructure will directly affect its ability to provide flexibility and growth. The more hosts/clients that a single file server can service, the greater the level of consolidation, connectivity, and management efficiency that can be attained. Further, as file systems are created, changed, and grown, it becomes necessary to balance the load across file servers in the infrastructure so that a single file server is not a chokepoint while others remain idle. For these reasons, it is generally less expensive overall to implement larger, faster file server systems that can share access to all the NAS information.

Example-E-commerce Web Site

The figure depicts a typical e-comrnerce web site as an example of an enterprise storage net work implementation.

This example demonstrates a combination of enterprise storage, SAN, and NAS. Web servers provide access to/from the Internet. E-commerce web pages will typically have both static (text, pictures, etc.) and dynamic (application specific or database) content. The static content is shared among all web servers and so is best implemented using a NAS architecture. In this example, the web servers are connected to the file server system by the back-end IP network switches. The dynamic content is provided to the web servers by application and database servers. These client server and database applications perform best when implemented on a SAN due to the dedicated storage access. It is also interesting to note that the NAS file servers themselves are also connected into the enterprise storage system through the SAN--demonstrating a complementary SAN/NAS architecture.

Enterprise storage networks are a marriage of enterprise storage, storage area networks, and network attached storage. While there is much debate as to the ultimate storage network technology winner (either SAN or NAS), it is more practical to consider where each technology can be best applied to achieve the information needs of the organization. It is often the case that the two represent complementary technologies. More importantly, it is important to understand the organizational forces that are driving the need to implement an enterprise storage network. The information infrastructure should then be designed leveraging the available storage, SAN, and NAS technologies to best meet the current and future needs of that organization.

Paul Ross is the manager of product marketing at EMC (Hopkinton, MA).