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Flash Solid State Disks: A New Breed of Enterprise-Class Storage
By Jun Alejo, BiTMICRO Networks

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SSDs in NAS, SAN Configurations

Data warehousing and data mining applications are important drivers for the NAS and SAN configurations. Data warehousing is built around relational databases while data mining is the process of retrieving warehoused information. The efficiency of a database is directly proportional with the speed at which files can be stored, sorted, indexed and retrieved.

The effectiveness of services offered by storage service providers (SSPs) depend not only on the availability of sufficient storage capacity, but also on their ability to provide the necessary I/O throughput and the transfer bandwidth required by multimedia services. SSDs can significantly improve the performance, efficiency and effectiveness of an external storage library. They can be attached directly to the library system or to the host system that is connected to the network. Figure 5 illustrates the two connection modes.

The degree of performance improvement achieved by using SSDs in NAS/SAN structures depends on system configuration, application and application workload. In the library-attached mode the database index files are stored in each storage battery's cache SSD, thus shortening the read access time between 10 percent and 80 percent, to nearly work memory performance levels. In the host-attached mode the cache SSD stores a smaller amount of index files, eliminating the time needed to transfer these files from the external storage to the work memory. The result is a significant host performance improvement, but only about a 10 percent to 20 percent read access time improvement. Obviously, the host-attached configuration is less expensive than the library-attached one.

Cache SSDs can be also used to store table files built from queries and to automatically update the dynamic table links of the relational databases. In the field of multimedia services, real-time A/V applications are the most demanding in terms of transfer performance. SSDs in A/V configurations enable the real-time delivery to subscribers of isochronous data for A/V services. These applications are viewed as key towards the further development of the Internet and the network access layer.

Most high performance mechanical storage devices can support the performance level required by one compressed video channel. If the same mechanical storage device contains multiple video selections, the HDD performance level would not be enough for the host server to switch in real-time between video selections.

SSDs provide the performance level that allows real-time low-latency switching between random video streams stored in the same storage device. This performance level satisfies the video-on-demand requirements for multiple subscribers. Further applications that can be satisfied are full-motion or freeze-frame video conferencing, A/V clip archiving and real-time A/V decompressing. Finally, SSDs can provide the performance needed for real-time video and animation requirements.

The upper part of Figure 6 shows an SSD used as the high-speed front end in a configuration that satisfies the video preview performance requirements. In this configuration, the SSD can store several minutes of multiple video selections clips to be visualized by users. Typically, one minute of an MPEG-2 compressed video file will require approximately 1 MB of storage.



The lower part of Figure 6 shows an SSD used as a high performance interim storage that improves the transfer bandwidth of the channel that delivers the decompressed video selection. The SSD access times are in the 30 to 50 nanoseconds (ns) range. This performance level can shift the video-on-demand performance bottleneck from the storage to the video server system, i.e., in a video-on-demand application the SSD storage will have to wait for the server, rather than the other way around.

Aside from the two configurations discussed above, more applications can be connected in NAS and SAN configurations and attached to a network.

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