Solid State Hard Drives
By Bryan Lambert – Sunday, January 11, 2009

There’s been a lot of hype lately about solid state hard drives as well as a lot of computers offering them as an option. What exactly are solid state hard drives, what are their pros and cons over standard mechanical hard drives? In this Tech Tip, we’ll take a look at these drives that seems to have mysteriously appeared on the scene in the last year.

Well…What are They?
So, exactly what are solid state hard drives? Quite simply, they are hard drives that use memory chips instead of a spinning platter that a standard mechanical hard drive would use. Often abbreviated as SSD, solid state drives have actually been around for a while, but have only started hitting it big on the consumer level in the last year or so. Some of the enterprise level (server room) solid state drives may use the same kind of memory that a computer uses as their main memory (called DRAM – which has to use a small battery to keep the contents intact), or flash memory chips (much like what is used in a digital camera or USB flash drive). Most solid state drives that are used in consumer level computers (the rest of us) use flash memory, so the remainder of this Tech Tip will deal with that type. So, let’s look at some pros for using solid state drives.

The Good

There are some very obvious advantages over a standard mechanical hard drive. First off, they’re solid state! That is, there are no moving parts, no spinning platter, no actuator arm, no motor, no nothing – just a bank of memory chips – this means that there is a much higher degree of mechanical reliability. Because they’re just a bank of chips, there is no time used to spin up the hard drive, it is just up and ready as soon as it is powered. Also, because there is no time spent for the actuator arm to read information off the platter, solid state drives can read much, much faster than a standard mechanical hard drive. Another nice advantage is because there is no spinning motor, there is no noise generated by the solid state drive (though some may incorporate a small cooling fan, that is nothing compared to the noise generated by a disc spinning at 7200 RPM). In addition, file fragmentation has very little impact on a solid state drive because of the very constant seek time performance of this type of drives. Solid state drives are also able to withstand shock and temperature extremes better than a mechanical drive, an important consideration if ever dropped.

The Not So Good

They wear out – or more to the point, the individual bits after a while can’t be erased and written to again. Flash memory quite simply has a limited number of times that information can be written to a location (a bit). Most consumer drives on the market today can handle about 10,000 writes to a bit. Once that spot is used up, it can never be used again. The good news is that there are a variety of techniques that engineers have developed to help combat this issue. The first thing is better flash chips. The chips used today are much better then the chips used in the first solid state drives that appeared a while ago on the enterprise level. Also, some drives employ extra memory chips to replace the bits that may go out. Many also employ wear leveling techniques that help wear the chips evenly. Another plus is that drives are larger and larger, so there are many of these bits to go around. Unfortunately, there doesn’t seem to be any consensus on what this means in practical, real world terms. How long will a drive last used with a standard operating systems, in a standard computer? Different sites have different answers, some saying as little as a year, while others up to five years (with normal usage).

There are also a few other cons to be aware of for flash based solid state drives. The first is that there are two primary types of flash memory used in solid state drives. The more prevalent MLC type tends to be slower, and have really long write times. In fact, the write times on MLC based drives are slower then standard hard drives and are not usually recommended for using as a primary drive with an operating system installed (but do work great as storage drives, because once that information is written, it can be retrieved very quickly). The other type (called SLC) has faster write times, but tends to be much more expensive than the MLC drives. This actually brings up the second point, even with costs coming down, even the cheapest MLC based solid state drive will be much more expensive than an equivalent sized mechanical drive (in fact, much, much more expensive) and the price differential really jumps with SLC based drives. Another point to consider is that solid state drives don’t have the capacity of mechanical drives, though the gap is rapidly closing. This means that you can pay the same amount of money for a 32GB solid state drive that you may be paying for a 320GB mechanical drive.

Final Thoughts