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SATA SSD Product Announcements – Pre/Post CES 2010

So far 2010 has been an active year for SSD product announcements and early evaluation snapshots. Several products based on SandForce controllers were announced while Micron and Marvell announced a 6Gbps SATAII drive that appears to have the performance lead. The primary flash suppliers see an opportunity to add higher value to the product line. Existing storage suppliers need to introduce new technology in the 15K rpm HDD space. Partnerships abound as each establish market presence. On the date of this post Seagate had not released the name of its 3rd-party controller although they are an investor in SandForce. It is an interesting strategy for Seagate as they own neither the Flash Translation Layer IP or the Flash IP for their Pulsar product.

A brief survey of announcements, specifications and early evaluations provides a perspective on the emerging landscape.

Overall product specifications were somewhat spotty as each vendor nails down their product definition for a target market. This post was not intended to be an extensive overview of the technology associated with using NAND flash as a storage drive but there are some important take-aways.

  • As expected SSDs significantly outperform HDDs on small block random performance. For 4K random short duration workloads an SSD drive provides roughly 100X IOPs over 15K HDD drives.
  • For 4K random longer duration workloads the advantage drops to 4X to 16X over 15K HDD drives. Controller workload for managing the write wear leveling, read disturbance and overall endurance of the NAND array increases over the life cycle of a SSD. A ‘clean’ SSD requires little to no endurance management as the next write can be written to an unused cell. As free cells are consumed and others released for erasure the endurance algorithm overhead increases and consumes controller resources, resulting in lower performance. This can be seen under Anandtech’s recent review of Micron’s RealSSD C300 from CES 2010. Random 4K writes peak early and after roughly 25 minutes or 75 Mbytes of data, drop sharply to a sustained level. Each vendor specifies this differently. Seagate specifies a ‘Peak’ performance level that can be achieved under shorter durations and corresponds to a clean SSD. Seagate also specifies a ‘Sustained’ performance level that may be seen if the workload consumes cells and results in higher endurance algorithm overhead. Some call this a ‘dirty’ SSD. Plextor has taken the approach of specifying a single performance number, whether ‘Clean or Dirty’. At first glance Plextor performance appears low, but when viewed in the context of Peak and Sustained characteristics for SSDs, may be sufficient for a particular system environment.
  • The comparison is missing warranty or MTTF life times. NAND flash does have finite Program-Erase cycles for both MLC (lower) and SLC (higher). By throttling the rate at which these cycles are consumed the life expectancy and time to BER uptick can be extended. I suspect each vendor is performing a rigorous reliability analysis to determine product specifications in this area. It is also possible that vendor-customer relationships drive a unique combination of performance and reliability operational points for a particular market.

In summary we are now seeing a richer selection of SSD products from flash vendors and traditional storage vendors who can supply OEMs at scale. SSDs will allow storage solutions to offer lower latency, especially random workloads. But as always, buyer beware. That 100X advantage over HDDs can disappear under some workloads. A thorough evaluation of the system level operational environment should be completed before deploying SSDs in production. A 10X SSD performance droop could present some interesting system level response time problems and obvious issues with management for spending large $$/GB for the latest / greatest storage.

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