The Ins And Outs Of Solid State Storage

The Ins And Outs Of Solid State Storage
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The benefits introduced by solid state drives are undeniable. However, there are a few pitfalls to consider when switching to this latest storage technology. This article provides a rundown for beginners and decision makers.

This article originally appeared here on Tom’s Hardware. It has been edited for the busy IT pro. Please see the original for details excluded here and for information on how to buy products featured herein.

Solid state drives (SSDs) seemingly have it all: storage capacities of up to 512 GB, blazing performance, low power consumption and heat, great efficiency, and incredible physical durability. In everyday life, SSDs seem all but perfect. But there are still some limits and pitfalls. We'll look at the details you need to know about SSD technology as it moves into a variety of applications at home and in businesses.

The SSD Market

First, we need to divide the market into segments. One way to approach this is to differentiate between low-cost, mainstream, and high-end offerings. This is typically what you find when searching for SSD reviews or doing price comparisons. Another method distinguishes consumer- from business-class products, roughly translating to client systems versus servers. Since the technology behind those two groups is similar, this article covers both worlds, pointing at individual aspects where necessary.

Business and enterprise products are typically not available in retail stores, as these target larger server and storage companies that assemble larger-scale systems. SSD makers, such as Samsung, Intel, Micron and Toshiba usually provide special support for solution providers. Samsung recently announced a partnership with Seagate to create enterprise-class SSDs. Clearly, the worlds of traditional magnetic and cutting-edge silicon storage are starting to mingle.

Trends and Developments

While the performance levels and efficiency of SSDs have developed quickly, capacities have not, owing to sluggish increases in NAND bit density. Huge demand from the smartphone sector has dragged on SSD evolution in PC environments. And the awaited transition to 3-bit cell flash memory is happening more slowly than expected. As a consequence, SSDs are getting more affordable, but it doesn’t seem like they'll escalate the capacity battle against hard drives any time soon.

Therefore, SSDs are expected to remain a minority player in the storage market compared to conventional hard drives. But 2010 marks the year in which SSDs achieved critical mass. Prices for entry-level products have come down to less than $99. On the enterprise side, power consumption should be considered. A 2008 study by McKinsey & Company found that data centers consume 0.5% of the world’s energy, causing more CO2 emissions than all of Argentina. The EPA estimates that data center energy consumption will reach 3% in the U.S. by 2011, making SSDs almost essential for keeping energy draw in check.

Getting an Overview

While enterprise and client SSD specifications don’t differ much, choosing the right drive or the right environment is very important. We will now look at how SSDs work, what they can do for you, where you should be careful when preparing for deployment, how your business will be impacted, and how to make proper buying decisions.

With the internal SSDs we're discussing today, flash memory and a controller are installed onto a printed circuit board (PCB) and packaged into a small enclosure. This housing is typically in one of the 1.8”, 2.5”, or 3.5” form factors that we all know and love from conventional hard drives. These can be mounted into PCs, laptops, or certain rackmount server environments. Indeed, flash SSDs look and largely behave like hard drives, with the exceptions that there are no moving parts and they weigh less. In addition, modern SSDs require very little cooling. Most SSDs employ a 2.5” housing and utilize 3 or 6Gb/s interface speeds.

MLC and SLC NAND Flash

Internally, all flash SSD products store data onto either single-layer cell (SLC) or multi-layer cell (MLC) NAND memory, able to store a single bit or multiple bits per cell, respectively. SLC cells offer less capacity per transistor than MLC, but higher write performance and data durability.

Modern Controller Architectures

All SSD designs are based on flash controllers that drive the storage circuits and connect to the host system via Serial ATA. Modern designs utilize the controller "brain" to tackle various needs. For example, data durability is addressed through wear leveling algorithms, ensuring that flash memory cell usage distribution is as even as possible to maximize the device’s life span. Performance is optimized through multiple flash memory channels, load balancing, and different methods of caching. Some controllers have an integrated cache, others work with a separate DRAM memory chip, and other designs utilize a part of the flash memory across multiple channels for data reorganization. Please read the article Tom’s Hardware’s Summer Guide: 17 SSDs Rounded Up for more details on architectures and specific products.

Trend: Toggle DDR NAND Flash

Samsung introduced Toggle DDR NAND flash memory a few months ago. This is a flash memory design that transfers data during the rising and falling edge of a memory signal, much like DDR DRAM. This approach debuted in the enterprise segment but will soon also be available in consumer SSDs. The main benefit of Toggle DDR is its increased bandwidth of 66 to 133 Mb/s per channel as opposed to 40 Mb/s. Drives using the new approach will probably not employ the faster peak bandwidth, but will instead try to maximize SATA II performance on 3 Gb/s interfaces while further lowering power consumption. We’ll explain in a bit why this is important.

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