Solid-state Drives Ready for Prime Time

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When asked about the reliability of NAND-based hard drives, Barnetson had no problem shrugging off fears of write corruption of failure. "Samsung's solid-state devices have a MTBF of approximately 1 to 2 million hours." Typical disk-based hard drives have a mean-time between failures of approximately 100,000 to 200,000 hours. Since there are no moving parts, the only real point of failure is for something to come unsoldered or a problem with the physical bit during a write.

Obviously, write-errors are a huge concern for those who have used flash products in the past. Only a few years ago the highest-end flash media was only useable for 1,000 or so writes. At that point the physical bits would "burnout" and could no longer be flipped. Today's single-level cell (SLC, memory that stores one bit per cell) is rated in excess of 100,000 hours before burnout. Multi-level cell flash, memory that stores multiple bits per cell, is significantly cheaper but even then is still rated at over 10,000 writes before burnout.

Is 10,000 writes enough? Absolutely, assures Barnetson. Samsung memory uses a technique called "wear leveling" to distribute the writes on a media through as many groups of cells as possible. Consider a typical computer that writes 120 megabytes per hour to the hard drive. On a 32GB solid-state NAND drive, wear leveling would distribute this data over the entire drive -- it would take 267 hours to fill the device once. Even on a multi-cell flash device, at this rate it would take no less than 150 years to burnout all the bits on the SSD. Single-cell drives are capable of ten times as many writes.

Even so, Samsung's initial solid-state drives are all single-cell designs. This first generation of SSDs are prohibitively expensive for most, but Samsung's SSD roadmap already has plans for multi-cell level drives as early as next year, which should bring the cost down considerably. Additionally, Samsung anticipates announcing drives in capacities of up to 128GB in early 2008.