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SUPPLEMENT SSD


deployments that demand consistent SSD performance. eMLC flash bridges endurance gaps at the expense of slower performance, since multiple read retries are required due to increased bit errors that occur over the life of the media.


Delivering Greater Endurance, Performance, and Reliability


with CellCare™ Technology The wide adoption of MLC flash in the consumer space makes it very attractive from a density and cost perspective. Performance, reliability, availability and endurance of MLC-based SSDs are directly dependent on the design of the SSD controller. The controller is the SSD brain and the main differentiator that determines behavior, performance and suitability of the SSD for enterprise applications. The controller responds to host commands, transfers data between the host and flash media, and manages the flash media to achieve high reliability and endurance.


How well a controller manages the flash memory determines whether the SSD can be used in enterprise applications that require 24/7/365 uninterrupted operations under heavy read and write workloads. STEC’s CellCare technology is designed for this specific purpose, making it the key ingredient for MLC flash-based, enterprise-class SSDs and provides three definitive benefits: (1) Improved endurance of MLC media; (2) Enhanced performance of MLC media; and (3) Reduced media access error rates and consistent performance over the useful life of the drive.


CellCare improves SSD endurance through the use of adaptive flash management algorithms. By proactively managing data cells throughout the life of the SSD, it provides improved reliability and reduced bit error rates. In addition, CellCare employs advanced signal processing techniques to dynamically manage flash wear which eliminates the need for read-retries by accessing error-free data, even at vendor-specified endurance limits. CellCare also employs techniques such as predictive read-optimization that ensures there is no loss of performance during the useful life of the drive.


Incorporating controller-based media access management, CellCare dynamically adjusts over the lifetime of the media to reduce the Uncorrectable Bit Error Rate (UBER) and advanced ECC techniques enable a higher degree of protection against media errors, leading to improved endurance of MLC flash media while maintaining high performance over the useful life of the drive.


As shown in Figure 2, neither MLC nor eMLC flash meet the endurance requirement of 10 full drive capacity writes per day.


As shown in Figure 3, MLC flash-based SSDs with STEC’s CellCare technology can sustain a rate of more than 10 full drive capacity writes per day for 5 years, without sacrificing performance.


Figure 3: MLC Flash-based SSDs with CellCare


Table 4 shows a cost/benefit comparison when CellCare technology is applied to MLC flash in SSDs and depicts that performance and endurance improves while implementation cost remains low.


Benefit Comparison Performance Endurance Better


MLC Flash eMLC Flash


MLC Flash with CellCare Technology


Low Low Best Better Best


Cost Low High


Best


Table 3: Benefit Comparison: MLC vs eMLC Flash vs MLC Flash with CellCare


Conclusion The reliability, availability and serviceability needs of a SSD are ultimately met by the SSD controller. STEC’s SSD controller, with integrated CellCare technology, provides enterprise-class endurance and improved performance for MLC flash media. This provides a cost-effective option to SLC flash-based solutions and provides IT managers with a choice for their specific enterprise application requirements.


The flexibility provided by enterprise-class MLC SSD alternatives enables OEMs to deploy these devices in the most demanding enterprise environments, leading to improved performance, higher reliability and reduced power, space, and energy consumption.


All of these factors contribute to lower total cost of ownership in SSD implementations for next-generation servers and data centers, compared to systems that rely on legacy hard disk drive technologies.


Figure 2: Flash Endurance vs. Technology Node SSD10 www.snseurope.info I October/November 2011


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