Solid-state storage update


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Solid-state storage is still mostly for well-heeled shops with power-hungry apps, but new developments could bring solid-state down to earth soon.

Solid-state storage received a big boost in 2009, with a large majority of storage vendors adding solid-state drive (SSD) options to their product lists. As a result, we've seen a sharp increase in the total number of enterprise-grade SSD components traded. A meager 59,000 units were sold worldwide in 2008, according to Stamford, Conn.-based Gartner Inc., but the total is expected to reach 5.1 million units and $2 billion in revenue by 2013. Although the price for NAND flash has come down by approximately 30% since last year -- with expectations that it will continue to decline annually at that rate -- it's still an order of magnitude more expensive than high-end disk drives. Because of its premium price, customers continue to deploy NAND flash judiciously, mostly for applications adverse to latency and requiring a high number of IOPs; in the past, expensive bulky arrays with a large number of spindles were the only alternative.

That's where solid-state storage shines today: A single enclosure of SSDs can displace a rack of high-end Fibre Channel (FC) drives at an overall lower cost, provide better performance, require significantly less power and space, and greatly reduce data center and operational complexity. Solid-state drives can also supplement disk arrays with a small amount of solid-state storage

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for frequently accessed data to boost array and application performance. OLTP apps like SAP and Oracle ERP, databases, email servers, high-transaction websites and even virtualization platforms are the great beneficiaries of solid-state storage. Whenever hard disk I/O and latency become the limiting factors, solid-state storage is an alternative. Conversely, and as a result of the high per-gigabyte cost of SSD, whenever large capacity is needed, hard disks continue to be the storage medium of choice.

Even though solid-state storage can be implemented with DRAM, NAND flash and other memory technologies, NAND flash is the prevailing solid-state drive memory technology in use today. In addition to non-volatile memory, enterprise-grade SSD products typically come with a small amount of DRAM that acts as write-buffer and cache, a controller with storage interfaces (FC, SATA or SAS) and software. Today, it's mostly the intelligence and proprietary algorithms in controllers that overcome the limitations of NAND flash, making it viable in the enterprise space. "Because of its better controller technology and algorithms to manage NAND flash, STEC [Inc.] has by far the largest number of design wins in the enterprise storage space today," said Joe Unsworth, research director in Gartner's Technology and Service Provider Group.

Glossary of SSD terms


Solid-state drives (SSDs): SSDs use memory chips, mostly non-volatile NAND flash, instead of rotating platters for data storage. The benefits of low latency, low power consumption and higher resilience compared to disk drives are a result of not having any mechanical parts.

Flash memory: Flash is non-volatile, rewritable memory. Unlike DRAM, it requires erasing blocks of data before they can be written to, resulting in a lower write than read performance. Depending on the technology, flash memory supports only a finite number of writes. Although flash memory is available as NOR or NAND flash, SSD products use NAND flash because it's more durable, less expensive, its cells are denser, and writing and erasing are quicker compared to NOR flash.

Single-Level Cell (SLC): SLC NAND flash stores one bit per cell. Because of its high endurance (approximately 100,000 writes per cell) and cost, SLC is predominantly used in enterprise-grade SSD offerings.

Multi-Level Cell (MLC): MLC NAND flash uses two bits per cell. With about one-tenth of the endurance of SLC NAND flash and a fraction of the cost of SLC flash, MLC is mostly used in consumer products. Newer 3-bit per cell (1,000 to 5,000 supported writes) and 4-bit per cell (a few hundred supported writes) NAND flash are targeted for applications with a very limited number of writes.


This was first published in September 2009

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