SSD 101

Introduction

An SSD offers some significant advantages for photographers and videographers, including extra speed, shock resistance, greatly reduced power draw, less heat generation, flexible form factor and potentially greater reliability. Compared to spinning disks, SSDs are only available in limited capacity (generally less than half that of spinning disks) and they command a relatively high price — more than four times the cost-per-gigabyte of a 2.5-inch disk.

SSDs are an area of fast growth, due to their several advantages. They are in increasingly common use for laptops and some desktop applications.

Just like a hard drive?


At first glance, an SSD will often look just like a hard drive. Many of them are in the same form factor as a laptop drive, and use the same SATA connectors. With a quality device and a modern operating system, an SSD can be swapped out for a hard drive with no particular configuration needed: just plug-and-play.

There are some issues to keep in mind, particularly in the purchase of an SSD. You’ll want to make sure you get a good quality device, and that you have configured your system so that it provides the maximum benefit for the premium cost it commands.

SSD basics


Every SSD has a few components in common.

• There is an array of flash memory, like that which is used in media cards.
• There is a controller that writes to and reads from the memory.
• There is a form factor, usually the same as that of a 2.5-inch hard drive.
• And there is a connection interface which connects the device to the computer or drive enclosure.

There are come commonalities in how SSDs function.

• In order to make the drive fast enough for usage, the controller must write to or read from multiple memory sectors on the drive simultaneously.
• Each bit on the drive will eventually wear out after it has been rewritten too many times. (Reading does not generally wear the drive out, only writing does).
• The controller uses a process called “wear-leveling” to spread the writing evenly across all the bits.
• Each drive comes with spare capacity that is used to replace worn-out bits.
• Modern SSDs use a process called TRIM to optimize performance of the drive as data is written, erased and rewritten.

Best uses for SSD

Solid-state drives are particularly useful for data storage made up of many small files, such as your boot drive or a Lightroom or Aperture catalog. These kinds of files can really slow down the throughput of a hard drive, since they require the read head to move to lots of different places on the disk to retrieve files. This is called “increased seek time.” An SSD drive can pull data from multiple places without having to wait for a component to physically move from one place to another, so it can speed up this process considerably.

Here are some good uses of SSDs:

• Use an SSD to hold your Lightroom or Aperture catalogs, or your video source files. These applications typically access smaller files and will benefit from the improved access time. This is probably the best use of an SSD for a photographer.
• Use an SSD to hold the system software and applications. The chief advantage is faster boot times, and some speed in general computing tasks.
• SSDs can also be used for storage of larger files, if the drive has fast sustained transfer rate and if your workflow requires high data throughput.
• SSDs are excellent for applications that need low power draw, such as ultra portable computers and netbooks.
• SSDs are extremely resistant to impact damage, so they are good in an environment where the drive may get bounced around a lot.

Which SSD?

There can be a big difference between a well-made SSD and a cheap one. The speed and durability of the memory chips and the quality of the controller can both make big differences in the quality of the device. Unlike hard disks, which must be made by a large manufacturer, SSDs can be assembled by much smaller companies that purchase the flash memory and a controller. Quality can vary widely.

SSD specifications look pretty different to those of a spinning disk. Here are some of the features to look out for:

Speed

There are two basic classes of speed that most photographers and videographers will want to looks at for SSDs.

Sustained reads/writes measures how fast the device can handle large files. This is important for people who expect to move a lot of large files through an SSD, or for people who will use the SSD for serving uncompressed video.

Random 4k reads/writes, on the other hand, measures how well the drive does with lots of small files, such as a Lightroom or Aperture catalog.

Controller

The controller is the brain of the SSD, as the name implies. When you buy an SSD, you’ll want to make sure the unit you get has a good controller. In most cases you should only buy a product where the controller is named as part of the specification. Do a web search on the controller model before purchase to make sure it has a good reputation. If you don’t want to go through that process, then the best approach is probably to simply buy from a good retail outlet that has knowledgeable customer service and a good return policy.

Good controllers include those from OCZ, Intel and Sandforce.

TRIM support

SSDs handle the deletion of data very differently from traditional hard drives, and it was common for early SSD units to slow down considerably after they had been in use for a while. The TRIM command (also referred to as “Garbage Collection”) was developed to address this problem, providing significantly better use of the drive as data is written, erased and overwritten. It is an OS-level tool, supported by Windows 7, Mac OS 10.6.6 and higher, and by Linux. Look for a drive that supports TRIM when you buy an SSD.

SSD and RAID

Because the TRIM command is generally not supported by RAID controllers, it’s probably best to avoid use of SSDs in hardware-controlled RAID configurations. If the RAID striping is done by the computer (“soft RAID”), then TRIM support is possible.

SSD and SMART

The Self Monitoring Analysis and Reporting Technology that was developed for hard drives has been extended for SSDs. Like traditional hard disks, the support of SMART data is not universal and varies by manufacturer.

Available Reserved Space – All SSDs come with spare capacity that is used to replace memory as it starts to become un-rewritable. The Available Reserved Space shows you how much of the original spare capacity is left.

Media Wearout indicator – This counts down the number of expected rewrites that the drive should support, starting from 100 when the drive is new and counting down to 0. Note that this is really telling you about the expected wearout, not the actual state of the internal memory.

SSD comparison websites

If you want to read more about the specific drives that are currently available on the market, we suggest that you check out the review sites that specialize in testing new hardware. Tom’s Hardware is a very good one, as is Adandtech.

Read more about SSDs at Tom’s Hardware

Read More about SSDs at ANANDTECH

PCIe SSDs

While the vast majority of solid-state drives connect like regular hard drives do, there is another configuration that promises even more speed, once it becomes well supported. Instead of putting the flash memory in a hard-drive-shaped box, it can be configured as a PCIe expansion card, and connect directly to the motherboard of a tower computer. In theory, this can greatly increase the speed with which the SSD communicates with the processor, providing a significant increase in speed.

For a PCIe-based SSD to function properly, the operating system will need to be configured to take advantage of the architecture. (This is similar to the way TRIM became necessary for conventional SSDs to work properly). While this architecture is on the bleeding edge right now, expect to see it become more common in the future.