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The emergence of ATA drives as a serious alternative to enterprise storage holds the promise of significantly reducing storage acquisition costs. This is amplified by the advent of Serial ATA, which brings features like hot-pluggability, CRC for all communications (including data, commands and status), and thin flexible cabling to further decrease the gap between ATA and more expensive "server" class drive. However, in order to fully realize the advantages of the ATA platform for enterprise storage, new software technologies are required to guarantee the reliability and maximize the performance of the platform.
Specifically, RAID technologies currently used with SCSI and Fibre Channel storage implementations are illsuited for use in the ATA arena. The pervasive use of write-back caching and the high cost of NVRAM-based board solutions negatively impacts the reliability and price advantages of the ATA platform, introducing the possibility of corruption and data loss and negating much of the cost benefit for the enterprise user. Similarly, the clear attractiveness of RAID Level 5 for large capacity storage is all but eliminated because existing methods for implementing low-cost RAID-5 systems have severe limitations in performance or reliability. On the ATA platform, this results in the undesirable flight to RAID-10 for most types of workloads and directly reduces the cost benefit of the platform.
In order for ATA-based storage to achieve its full potential in the enterprise, it is necessary to understand the limitations of today's hardware-assisted RAID solutions as these attempt, imperfectly, to address the unique characteristics of the ATA drive platform. Particular attention is placed on RAID Level 5, which is the most promising RAID type given its natural application to the larger capacity storage applications that will dominate networked ATA adoption.
ATA Characteristics
ATA disk drives emerged in the late 1980s, as desktop computers began their ascent into the mainstream of the IT universe. ATA is an acronym that stands for "AT Attachment," a reference to the IBM PC/AT that served as the de facto reference specification for the desktop since its introduction in the early 1980s. Though synonymous with IDE (Integrated Drive Electronics), the ATA designation is the subject of various ANSI specifications that have evolved the platform over time and is generic to the category.
Since their initial shipments in 1986,...