Due to the growth of video on demand (VoD), IPTV media content, and embedded database applications, AdvancedTCA (ATCA)-based storage capacity requirements continue to increase exponentially. In addition, storage requirements have become more complex and varied for ATCA designs that have expanded beyond the central office to include network data center and general data center applications that need to handle a wide variety of server platforms. The advancements and general availability of new storage solutions, particularly solid state drives (SSDs), enables ATCA platform developers to meet the design metrics of a broader range of markets where distributed data storage and management become increasingly required. The continual evolution of SSD storage technology, with its improved capacity, performance, and cost reductions, provides additional opportunities for integrating storage directly into the ATCA platform, allowing new designs to gain the benefit of high performance and availability provided by ATCA-based systems.
Complex Storage Considerations
The expansion of the storage industry has placed higher expectations on the role and performance of the storage subsystem in ATCA-based applications. In VoD, IPTV, and billing/authorization applications there is a customer expectation of, and therefore a need for, instant access to distributed data over a network. This puts storage performance at a premium. This higher performance requirement is further challenged by the finite power and space limitations in most ATCA-based systems that live in a data center or other restricted environment.
A good solution for this dilemma, in light of the multiple storage technologies available to designers, is to integrate a group of cascading hard disk drives (HDDs) with several SSDs to get the job done. Utilizing both storage mediums to their fullest within the required performance, power, and size design specifications allows faster, multi-user data access to “hot data” with an SSD that excels at read performance while relying on HDDs to handle the mass storage load. Because they have no moving parts, SSDs do not have latency issues, so they perform very well in applications with significant amounts of random data. These applications can also benefit from employing a combination of both HDDs and SSDs to intelligently manage how data is written so as not to wear out the SSD and maximize its endurance. SSDs provide the needed high random read performance and fast access to random unstructured data for multi-user environments that demand the highest reliability and data integrity.
This tiered storage approach provides an ideal symbiotic relationship where SSDs act as performance enhancements to a hard drive-based subsystem allowing the most popular content to be accessed quickly, making for a more application-centric distribution of storage. Big storage libraries can strategically use SSDs to enable customers to connect on demand, providing the five-9s (99.999%) availability that must be achieved.
ATCA Application Storage Requirements
While the individual specifications vary for ATCA designs, all have common needs for enhanced lifecycle, low power, standards compatibility, temperature, and acoustical requirements. Storage is no exception, and a tiered storage approach provides the solution to match these requirements.
Virtually all central office, network, and data center types of applications have long product life requirements that ideally would last 10 years, and this need certainly extends to ATCA-based VoD, IPTV, and billing/authorization systems. Adding SSDs to the storage equation extends the life of storage subsystems through wear-leveling, error correction and other integrated data retention technologies that have proven to maximize drive endurance. JEDEC is the main standards body for NAND flash characterization. When NAND flash vendors specify their endurance and data retention, they do so relative to the following JEDEC standard:
Data retention = 10 years at 10% of the endurance rating.
Data retention = 1 year at 100% of the endurance rating.
SSDs also help to enhance product longevity through their inherent ruggedness and reliability through adherence to shock and vibration standards.
Low power and high IOPS (Input/ Output Operations per Second) performance per watt are critical metrics for ATCA storage because the power budget is usually a fixed element within an ATCA system. Using HDDs for capacity and SSDs for performance allows designers to optimize performance for their power budget, which is typically less than 10W per 100,000 IOPS. In addition, by taking advantage of lower power SSDs, thermal management is more easily controlled for the entire storage sub-system.
To further support the performance enhancements available from new host system interfaces, storage solutions must keep pace and be compatible with the latest standard interfaces such as SerialATA (SATA), Serial Attached SCSI (SAS), and PCIexpress. Designers will find that they have a wealth of storage choices from manufacturers of both HDDs and SSDs.
Acoustic requirements come into play for ATCA systems to satisfy the demand for more silent system operation, especially in digital recording applications that must keep audible noise to an absolute minimum. SSDs with no moving parts are an obvious choice for these applications, and there are new HDD advancements that help reduce noise. For instance, the new smaller 2.5-inch HDD form factor coupled with an enhanced bearing design, application-specific seek algorithms, and slower rotational speeds can provide a much quieter solution.
Probably one of the most important evaluation criteria used today for embedded systems development is total cost of ownership. Minimizing total cost of ownership is critical for embedded ATCA-based systems and storage is no exception. Every design has a “storage budget,” which is the sum of all types of storage in an application. Optimizing performance and reliability within the storage budget by matching storage technology to usage model is a significant way to reduce total cost of ownership and increase customer satisfaction.
The first place most companies start in their storage evaluation process is to target the ideal capacity point and evaluate the dollars per GB in a given footprint. While this is a good place to begin and works well to determine the best storage value for a desktop or notebook PC, it is not the only measure for embedded systems. Designers of ATCA systems, however, may be more concerned with unit cost (i.e. if a $50, 8GB SSD does the job and provides the needed capacity, it is a better value than a $60, 200GB 2.5inch notebook HDD). Price per GB is higher, but price per unit, which is the key metric in this case, is lower because both offer enough capacity.
Most embedded systems are also concerned with power budgets so metrics like GB per watt, IOPS per watt or speed per watt have become important evaluation criteria.
If evaluating the storage solution purely on GB per dollar, HDD technology will remain the clear winner, but when discussing capacity per watt, SSDs perform very well. In terms of IOPS metrics, SSDs tuned for such applications come out on top. Beware that there is little commonality in the way storage vendors specify IOPS. The IOPS metric varies greatly depending on file size, command queuing, the mix of reads and writes and whether or not some level of DRAM cache is enabled. While some vendors specify read IOPS, others specify write IOPS and some total read and write IOPS. Capitalizing on the inherent benefits of both HDDs and SSDs will, in most cases, allow designers to reach their IOPS per dollar and IOPS per watt storage goals.
The IOMeter benchmark is seen as the industry standard benchmark that allows users the needed flexibility to configure the workload to more closely match the application. In addition, industry trade associations and standards committees such as JEDEC JC-64.8 and SNIA’s Solid-State Storage Initiative (SSSI) have begun to tackle the important issues of driving performance characteristics and lifecycle management to give designers a clear and consistent way to evaluate storage.
Putting a Tiered Storage Solution to Work
Using a network Digital Video Recorder (DVR) application as a good example of an ATCA-based system, the storage subsystem is further challenged by an application that is typically controlled by the service provider instead of an end box. In this environment, the storage solution must contend with immense content and fast transport requirements while maximizing system up-time and minimizing service call issues to adequately deliver the capacity, performance and reliability demanded. That is why a combined HDD and SSD solution is the optimal choice for a DVR application. The HDDs provide the high capacity storage that meets the GB per dollar budget. SSDs, on the other hand, provide the performance IOPS and low-power operation required for transport of on-demand content while meeting the IOPS per dollar and IOPS per watt metric. And because SSDs only wear electrically for writes and are virtually impervious to shock and vibration issues, reliability and up-time are assured.