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Solid State Drive (SSD) Buying Guide

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In October, we reported that industry experts predicted SSD prices to fall as thinner and newer NAND flash memory chips rolled out. With the introduction of the new Samsung 850 EVO SSD featuring 3D V-NAND, those industry predictions seem to be coming true. On top of that, Intel very recently announced they will begin mass producing 3-bit 3D V-NAND. With V-NAND SSDs finally releasing and prices of drives dropping, an SSD should be on your to-buy list soon.

As for which SSD to purchase, several factors and metrics should be prominent in your decision-making process. To help you choose the right SSD for your needs, those factors and metrics are outlined in the SSD buying guide below.

NAND Type

The type of NAND used in a SSD matters—a whole lot, in fact. But what is NAND? NAND is a type of non-volatile flash memory, meaning it does not require power to retain or store data. Devices such as digital cameras, USB flash drives, smartphones, and SSDs utilize NAND flash memory for storage.

NAND falls into several types: single-level cell (SLC), multi-level cell (MLC), enterprise MLC (eMLC), triple-level cell (TLC), Redundant Array of Independent NAND (RAIN), and the new 3D vertical NAND (3D V-NAND).

  • SLC – A type of high-performance NAND flash memory that costs more than other types of flash memory to manufacture. SSDs with NAND memory chips never gained mass appeal due to high per-GB prices, and are found mainly in enterprise-grade SSDs. Also, SLC memory chips feature better write/rewrite endurance than MLC, meaning data can be written and rewritten before performance degrades. Few mainstream SSDs utilize SLC memory chips.
    • Pros: Faster performance, better write endurance
    • Cons: Higher price
  • MLC – For the last few years, MLC was the go-to choice for storage manufacturers to use in solid state drives. While slightly slower than SLC memory, MLC could be produced at much lower cost and therefore was the primary type of NAND flash memory used in SSDs.
    • Pros: Lower price
    • Cons: Slower performance
  • eMLC – A type of MLC NAND aimed towards light enterprise use or high-end mainstream use. Features higher write/rewrite endurance than MLC, but lower than SLC. A lower cost alternative to SLC.
    • Pros: Lower cost than SLC, faster performance than MLC
    • Cons: Higher price than MLC, lower endurance than SLC
  • TLC – A type of MLC designed for use in budget-oriented SSDs. TLC flash memory features lower write/rewrite endurance than MLC. With a low per-GB cost, TLC SSDs make a strong case for value.
    • Pros: Lower prices than MLC
    • Cons: Performance slightly slower than MLC, lowest write endurance
  • RAIN – Unsurprisingly, many users do not know the term RAIN NAND, as few SSDs utilize RAIN NAND flash memory. But many are familiar with the term RAID, or Redundant Array of Independent Disks. RAIN is a similar concept to a type of RAID configuration, but applied to SSDs. Without getting into the technical details, RAIN NAND is designed to offer higher reliability and endurance rates.
    • Pros: Better reliability and read/write endurance
    • Cons: Slightly higher prices
  • 3D V-NAND – The proverbial new kid on the block, 3D V-NAND represents the latest iteration of MLC technology. Instead of having flash memory cells stacked horizontally, V-NAND technology stacks memory cells vertically. To use an analogy, imagine a neighborhood. Traditional MLC SSDs represent a suburb with many single- or two-story houses. V-NAND is a neighborhood of high-rise apartment buildings. For the buyer, V-NAND allows for high SSD storage capacities without a dramatic increase in price.
    • Pros: Larger storage capacities, lower prices
    • Cons: Performance on par with TLC SSDs and slightly slower than MLC

Memory Controller

NAND flash memory cells do not exist in a vacuum inside a SSD. Every SSD features a controller chip that manages data on the memory cells and communicates the other components on the computer, such as the motherboard and other data storage devices. Memory controllers handle many prominent features found in SSDs, such as wear-leveling, reading data, writing data, data provisioning, and more. Because of that, the type of memory controller used can impact drive performance, reliability, endurance, and other extraneous features.

Determining the best memory controller can be difficult, especially as they generally perform well. However, it is wise to check forums or do a general web search for the memory controller used in a SSD you may be interested in purchasing. By doing this research, you may uncover reliability issues, necessary firmware updates, known compatibility issues, or more. For example, cursory research into SandForce flash memory controllers reveal that the first generation suffered from compatibility issues with the Intel® Haswell platform and some users of the SF-2000 series reported freezing and blue screens of death.

Drive Performance

Consumers shopping for SSDs and hard drives frequently pay close attention to SSD throughput, more commonly presented as read/write rate, as the key factor in determining drive performance. While true, read/write rates do affect the speed of writing and reading files to and from the drive—they do not matter significantly. Throughput matters primarily when transferring a large amount of data on or off the drive.

So what is the metric that measures SSD performance?  Input/Output operations per second, or IOPS.
“The most important thing is the IOPS,” says  Jason Chen, NeweggBusiness Merchandising Manager for SSD.” That’s the random pings to the drive.  This gauges the speed since real-world OSes constantly ping the drive for small amount of data instead of large amounts.” IOPS indicates how often a SSD can perform a data transfer every second. Often overlooked, IOPS serves as a better metric for drive performance than throughput. For enterprises, it translates into how often and quickly data can be accessed in a multiple user setting.
When comparing SSDs, put a higher priority on IOPS than on read/write rates, as high IOPS has more of a performance impact.

Capacity

Your ideal SSD capacity depends largely on your usage scenario. In the current market, SSDs generally range from 120 or 128 GB at the low end all the way to 800 GB or larger. 1 TB SSDs exist, but primarily for datacenter and other enterprise applications. Industry expert Jason Chen says disks in the 256 GB range serve well for purchasers looking to future proof their systems.

That middle ground will likely shift as V-NAND becomes more popular, but TB SSDs will not likely be mainstream for some time to come.

Interface Type

The majority of SSDs at the moment utilize SATA III as their data interface. Other less common types include PCI Express and mobile SATA (mSATA). Generally faster, PCI Express SSDs do not make up a significant portion of the SSD market. However, industry prognosticators such as Chen believe adoption rates for PCIe SSDs will likely increase in the future.

On the mobile side of things, purchasers have a relative large selection of mSATA drives to shop. Size-wise, mSATA drives are comparable to business cards and typically lack plastic/metal housing or shells. For Ultrabook™ owners looking to upgrade their SSDs, mSATA is typically a requirement.

Armed with the information above, shopping for a SSD should be a swifter process. Find one with the appropriate type of flash memory, size, performance, and interface type required for your usage scenario.

We hope our SSD Buying Guide helps you with your decision to upgrade your system.

Photo by Hong Chang Bum, taken from Flickr Creative Commons
Wallace Chu

Wallace Chu

A self-professed tech hipster that loves computers and music. Uses an iPhone ironically.

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