RAID and the SAN.

The hottest topic to hit the computer industry in a long time is SAN. A SAN is basically a network of storage devices, whether they are JBODs or RAIDs, that are all linked together and can be accessed from multiple servers. It is the same concept as linking servers and workstations together in a LAN/WAN network environment, but carries it to the next level--a Storage Area Network.

The concept of SAN breaks away from the traditional network environment. In the past, storage devices were attached to the network via an available server. This limited the data that could be housed on a particular storage device. Since the server would run a designated operating system, the storage device that was attached to that server would only be able to store information from that operating system. A SAN environment changes that concept entirely; multiple servers with different operating systems can share the same storage devices.

To enhance this new SAN technology and speed up the time required to access data, the industry was also developing a faster interconnect between network storage devices that would allow data to be transferred between servers and storage with few network bottlenecks. That interconnect is Fibre Channel. Still in its initial stages, Fibre Channel offers up to 100MB/sec transfer rates with the promise of faster speeds in the near future. This provided just the right medium to solve the interconnect network problems. SANs utilizing Fibre Channel enable numerous storage devices to be located in remote locations and allow many servers with multiple operating systems to access these storage devices. SANs will also allow for easier storage management from one single point in the network, a dream that MIS professionals have had for a long time.

Why Include RAID In The SAN?

Why should I use RAID technology with my SAN solution when I could just as easily add hard drives when I need more storage? First, your organization should consider RAID if data integrity and redundancy are important issues. Secondly, you should consider RAID if you are finding your company's storage requirements are growing at an exponential rate. Finally, RAID would be an optimal choice if you want to increase access speed to your company's shared storage.

The following are the main benefits that system administrators will want to look for when evaluating a storage system for their SAN solution.

1. Protection of investment

2. Scalability

3. Density

4. Data redundancy 

5. Controller redundancy

6. Power redundancy

7. Modularity

8. Support

9. Low cost/megabyte

10. Full RAID level support (level 0,1,3,5, and 0+1)

Additional RAID Requirements To Consider For SAN Environments

* RAID Caching. To improve data access for SAN environments, RAID controller manufacturers add cache memory on the controller board to temporarily store data. Since data is usually accessed in a sequential manner, some of that data could be stored in (much faster) RAM memory. If the data required is stored in cache, then the controller quickly retrieves it. If it is not in the cache, then the controller will then have to go to the drives to pick up and reassemble the data. There is, however, a slight performance hit in this scenario. Therefore, the larger the cache the better; however, cache memory is expensive and there is an economic trade off. The object is to have enough cache memory to increase performance with minimal impact on overall price.

* RAIDsets. A RAIDset is a specific RAID level, set to a number of drives in a RAID system. A system with multiple drives could accept numerous RAIDsets. In a SAN environment, MIS administrators can set various RAIDsets on multiple RAID systems to manage various types of data. One RAIDset could be set to RAID level 3 and could use 4 drives to hold database information; while another could be set to RAID level 5 and could use another 4 drives to hold accounting information.

* Platform Independence. In today's age of multiple platform environments, RAID systems must be able to work on any operating system and any computer platform. This is the basic premise of the SAN environment--no matter what operating system a department or workgroup in an organization is running; they will all have access to the company's centralized Storage Area Network. With platforms such as NT, Unix, Mac, and Linux being used widely across organizations at the same time, having a storage system that can interact with them all will prove to be invaluable.

Richard Eng is the director of sales at Integrix, Inc. (Newbury Park, CA).