Solid State Drives (SSDs) are faster, more rugged, and (presently) more expensive than Hard Disk Drives (HDDs). When SSDs are priced competitively to HDDs, we will begin to see every PC equipped with an SSD for long-term storage, because SSDs are suitable for a decade or more of typical consumer use. SSD is just Flash memory.
A Flash (NAND) memory read is faster than a memory write (a.k.a. a memory program) and causes less wear than a program. This is because, in order to program to NAND memory, you have to erase it first. This also means that writing to an SSD takes longer than reading. Most SSDs for PCs are very large, and manufacturers use techniques to make them wear evenly. The methods may include read/write (R/W, a.k.a program/read) cycles applied across the entire expanse of memory, compression algorithms that make the R/W less intensive (but create some latency as compressed files are packed and unpacked), and overprovisioning (more Flash than advertised so warnings can be issued before failure occurs). Modern SSDs will retire a block of memory as it fails, reallocating the contents to another location, as well. And although you need not worry about the “bad sectors” issue that can happen with HDDs, the equivalent in uncorrectable errors is possible with SSDs after a few hundred terabytes of R/W action.
Size and quality matter
However, like the adage, “you get what you pay for,” Not all SSDs offer the same features. Although sheer size is an overall benefit because a larger SSD has more blocks to spread wear, your purchase should reflect not only your usage patterns for the drive but the quality of engineering and forethought that goes into how the SSD is managed throughout its lifetime. All other things being equal, the larger the drive, the longer the SSD will live. How you plan to use the drive also matters. If the SSD is used like a DVR or TiVo device that continually records shows on a regular basis, the SSD will wear faster. However, it takes hundreds of terabytes of program/read cycles to kill most SSDs. Therefore, if you plan to use an SSD as a DVR, it is reasonable to expect that you will see a decade or more of life out of that SSD. Unlike HDD’s, we have seen impressive and continual improvement in flash memory over the years. Therefore, by the time a decade has passed, you may already be eyeing the latest storage technology, anyway.
SSDs have a faster load time than HDDs, but you will not see a performance increase on everything to do with storage. A computer with an SSD instead of an HDD will boot up faster, but Frames Per Second (FPS) in gaming is not improved by an SSD as much as a good GPU. An SSD cache is good enough for many applications because the cache will be loaded for quick access to everything you need for the application to run swiftly. If you are worried about SSD in general and not the early-adopter type, try an SSD cache with an HDD as main storage. SSDs (or NAND flash in general, including USB drives) should not be used for long-term storage (10 – 20 years or more). For long-term storage, also called “cold storage,” data should be transferred to optical media such as Blue-ray which has an estimated
lifetime of at least 50 years.[i] Magnetic tape is another cold storage option. Fresh NAND flash memory will retain data longer than NAND flash memory that has withstood many program/erase cycles, however.[ii]
SSDs are different: what about Secure Erase?
One of the significant differences between HDD and SSD is in securely (completely) erasing data because they store data in a different manner. An HDD can be forensically erased with a good program that promises a “secure erase.” Therefore, to securely erase an SSD, the program promising the secure erase must have been programmed with SSD, not HDD, in mind. The SSD manufacturer that offers a secure erase option for its drive is a better choice than a random utility program that does not explicitly offer a flash-based secure erase option. Overwriting an SSD twice is good, but does not always work, and the overwrite pattern can lend forensic clues. To further obfuscate matters, not all SSDs are created alike, so a secure erase technique performed on one may not work on another. According to research, only an ATA Secure Erase command that is correctly implemented can reliably sanitize an SSD.[iii]
Ruggedness: sand or rust?
The difference between the SSD and HDD comes down to materials; one is based on metals that can be magnetized (HDD), and the other is based on silicon (SSD). HDD is a spinning disk of metal. A spinning disk requires a spindle, bearings, and a stepper motor, among other things. SSDs have no moving parts, are less susceptible to harsh environments than an HDD, and, all other things being equal (like contact points/connections) are always going to be more rugged as installed due to fewer moving parts. HDDs can form corrosion on the surface of the platter, usually rust.
For a short time in the old days, people had to “park” the head on their HDDs before physically moving a PC that was still turned on. Like a needle on a turntable, the head could damage the HDD if it was bumped or moved during operation. HDDs are still parked, but automatically by using an accelerometer to detect movement within microseconds so the HDD can be parked.
The aging SSD
An SSD can age prematurely if someone hacks your PC and makes it continually program/read for a year and a half or more without you noticing. That’s how long it took for the guys at The Tech Report to get the first of several SSDs to fail after constant program/reads in their 2015 SSD Endurance Experiment. After every 100TB (100,000 GB) of transferred data, The Tech Report checked each drive. Of all six SSDs that they tested, three lasted beyond one PB (one million gigabytes) of cycles and all six made it past 700 TBs before failing. The report was written in 2015, and SSDs have improved since then. However, the conclusion is that normal consumer behavior does not challenge a modern SSD. All of the SSDs logged reallocated memory cells as failures mounted, and not all failed catastrophically without warning.[iv]
Conclusion
The modern SSD is well-equipped to handle typical consumer needs for more than a decade. SSDs are much more rugged than HDDs and cannot be securely erased in the same manner as an HDD. SSDs do not become appreciably slower as they age, since data is reallocated to good memory blocks as needed. Choose an SSD that is a little larger than what you think you will need, keeping in mind that the SSD can last up to hundreds to TBs of program/read cycles before failing. You do run a risk of suddenly and catastrophically losing data in an SSD that has withstood hundreds of TBs of program/read cycles. However, you are going to get several warnings before that happens (assuming your computer system “knows” you have an SSD or that you can check the drive logs periodically). SSDs are not intended for use as cold storage, however. Do not use an SSD to store data for the long-term (more than ten years) without moving it to another SSD, a Blue-ray disk, or magnetic tape. To prolong the life of your SSD, do not continually subject it to continuous program/reads (e.g., avoid volunteering as a torrent site), do not defragment it, and avoid malicious viruses that could subject the SSD to continuous program/read cycles.
Protect your SSD life by protecting yourself from viruses and hackers, keep your operating system up to date, and avoid activities with exhaustive program/read cycles. The latter means avoiding running SSD benchmark tests, avoiding supporting a torrent site by lending your PC to it, and avoiding PC hibernation (or other actions that store to the SSD on a regular basis that you don’t really need). Keep in mind that an SSD is going to last a long time unless you are using it for something unusually R/W intensive.
[i] https://www.forbes.com/sites/tomcoughlin/2014/06/29/keeping-data-for-a-long-time/#7f82e04c15e2
[ii] http://ieeexplore.ieee.org/document/7574572/
[iii] http://eecatalog.com/caciufo/
[iv] https://techreport.com/review/26523/the-ssd-endurance-experiment-casualties-on-the-way-to-a-petabyte
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