The advent of solid state drive (SSD) in the last few years as a viable alternative to the traditional hard drive (HDD) providing a much higher speed than the latter and other considerable advantages, has built up the reputation of this flash-based storage technology so quickly to the point that so many IT professionals were impelled to deeming it “the best performance upgrade” and recommending it to everyone looking forward to take their computer to the next level. That’s because, unlike solid state drives, no single hardware upgrade is capable of offering the kind of instantaneous and observable boost in system responsiveness, compared to a system based on traditional hard drive spinning media.
Yes, it’s true that a faster processor, additional memory, and a faster graphics card may notably better the overall system performance, but compared to what an SSD can do, all those upgrades fall behind.
But all the stated above traits don’t make SSDs free of disadvantages, they already undergo their own, and we’ll be outlining those disadvantages within this article after addressing the outstanding advantages they boast of.
The Advantages of SSDs
There are many advantages solid state drives (SSD) have over traditional mechanical hard disk drives (HDD). The majority of these advantages are resulted from the fact that SSDs don’t employ any moving part in their architecture. In contrast to mechanical hard drives that use drive motors to help spin up the magnetic platters as well as the drive heads, flash memory chips are the ones responsible for all the storage on a solid state drive. This feature offers faster data access, lower power requirements, and high reliability.
Because SSDs don’t have any moving part, they are nearly invulnerable to fail in high shock and vibration environments and extreme temperatures. This trait, particularly the potential of operating in extreme temperatures between 0°C to +70°C, allows an SSD-based system to handle more applications in difficult situations where the traditional hard drives fail.
Also, for portable systems, reliability is an important factor. It’s very likely that traditional HDD is seriously affected when exposed to jarring movements from an impact. The advantage of SSD here explicitly appears, because an SSD stores all its data in memory chips, therefore in the event of an impact there are no moving parts to be damaged. The risk of mechanical failure is almost completely eliminated by this lack of moving parts. Table-1 compares the key features of reliability on SSD, standard HDD and an extended temperature HDD. Using these features helps specifying which particular hard drive will be suitable for a particular application environment.
Data Read & Write Rates
As far as measurement, testing and industrial applications are concerned, Data access rates are intensively important. Since the SSD does not need to move the drive heads or spin-up the drive platter as in the case of traditional HDD, data in an SSD can be accessed almost promptly. Due to the lack of these mechanical delays, SSD exhibit significant increase in the read/write rates. This performance boost adds to user productivity by enabling increased data read and write rates, faster loading of applications, and decreased system boot-up/shutdown time. Refer to table-2 for comparison of data transfer rates for the SSDs and regular HDDs.
It’s not only that SSDs have faster read and write rates than traditional hard drives, but also they have better deterministic performance. Unlike regular HDDs, the performance of an SLC SSD is almost constant and deterministic across the entire storage space. This is because of the constant seek times offered by a solid-state drive.
This performance advantage is due to two key reasons. The first of them is file fragmentation. Over time files become more fragmented, requiring a regular HDD to perform additional seeks to retrieve an entire file. This process decreases the effective performance of the drive as compared to the SSD, which has way lower seek times.
The second reason is the method in which data is stored on an HDD. When data gets first written to an HDD, it is stored in the sectors close to the outer edge of the spinning platters, which move faster as compared to the sectors nearer to the center of the platter. But when the HDD fills up, the situation differs and data is written to the slower-moving inner sectors, decreasing write and read speeds up to 50%. Here where SSDs have an advantage for not having moving parts. They are able to maintain the same level of read and write performance through the entire capacity of the drive.
Figure 1 compares the performance of the Seagate 2.5in SATA Extended Temp HDD and the Samsung 2.5in SATA SLC SSD reading data across the entire disk. As the graphs illustrate, as you move from the outermost rim to the inner rim of the traditional HDD there is a significant drop in read rates, whereas the rates remain fairly constant for the SSD.
For portable systems, power consumption is an important factor. SSD uses far less energy than regular traditional HDDs as there is no power used to drive motors in a SSD. The traditional hard disk industry has taken steps to address power requirements of traditional drives by implementing idle drive spin down and the development of hybrid HDDs, but even with both of these implementations, regular HDDs consume more power than a SSD. Table 3 compares the power consumption for the SSD, standard HDD and an extended temperature HDD.
The Disadvantages of SSDs
Switching over from the current hard disk drive to a solid-state drive seems an appealing step. But before you take any action in this regard you should realize that SSDs are not free of downsides/disadvantages, such as their steep prices. Even after the dramatic price fall of NAND flash memory, SSD is still deemed expensive. See for example the price of the cheapest 1 TB SSD, which is Samsung 840 Evo, it costs on Amazon by the time of writing $431, that indicates $0.43 per GB, whereas the cost of Western Digital 4TB Black is almost $230, and that indicates $0.0575 per GB, a real vast difference.
Then there’s the issue of longevity. The NAND flash used in SSDs can only be used for a finite number of writes. Why? Because SSDs can’t write a single bit of information without first erasing and then rewriting very large blocks of data at one time. Each time a cell goes through an erase cycle, some charge is left in the floating-gate transistor, which changes its resistance. As the resistance builds, the amount of current required to change the gate increases. Eventually, the gate can’t be flipped at all, rendering it useless. This decaying process doesn’t affect the read capabilities of SSD, because reading only requires checking, not changing, the voltages of cells. As a result, NAND flash can “rot” into a read-only state.
Some manufacturers use something called wear-leveling to counteract the degradation of NAND flash. This technique distributes data writes across all blocks to make sure the flash memory wears evenly, but even with that, SSDs will decay over time. NAND flash memory of the single-level cell variety generally delivers 50,000 program/erase cycles. Flash of the multi-level cell variety — the kind used in consumer-level products — wears out after about 5,000 cycles.
Rest assured though, that was the situation of the first, old-fashioned solid-state drives, but modern ones, especially the top quality SSDs come with real high endurance that can handle the toughest cases, and for that reason their manufacturers provide a 5-year warranty on them.
But still, even though modern SSDs are very durable, the high price and low capacity poses a problem, and for that reason many data centers and techies use a combination of SSD and HDD. One approach is to use a solid-state drive in a laptop and a traditional hard drive as external storage holding music, photos and other files. This combines the best of both worlds — the ultrafast, random data access of SSD with the relatively inexpensive, high capacity of HDD. If this sounds good to you, you’ll want to start shopping for a suitable solid-state drive. Leading manufacturers include Samsung, Seagate, SanDisk, Corsair, Toshiba and OCZ Technology. And don’t forget about Intel, which offers a robust line of drives, as well as several tools to help you choose the right technology and calculate how much time and money you can save if you make the switch to SSD.