Investigation: Is Your SSD More Reliable Than A Hard Drive?

Does a lack of moving parts translate to higher reliability? That's the assumption many enthusiasts and IT professionals make about SSDs. We go straight to the data centers using these devices, dig into failure rate statistics, and suggest otherwise.

Back in 2008, Intel made a case to us about storage bottlenecking its Nehalem architecture. We were at IDF in San Francisco, the company was introducing its first solid-state drives, and its representatives stood on stage, describing the ways in which a conventional hard drive slowed down a Core i7 processor. Three years later, we've seen over and over in benchmarks that SSDs are legitimate performance-adders, changing the computing experience fairly dramatically.

With that said, performance isn’t everything. When it comes to your data, all of the speed in the world means little if you can't trust the device holding that important information. After all, when you read about Corsair's Force 3 recall, OCZ's firmware updates to prevent BSODs, Crucial's link power management issues, and Intel's SSD 320 that loses capacity after a power failure, all within a two-month period, you have to acknowledge that we're dealing with a technology that's simply a lot newer (and consequently less mature) than mechanical storage.

This topic is even more relevant now, in the wake of a swift shift from 3x nm NAND to flash memory manufactured at 25 nm. We've talked to some very bright minds in solid-state drive design, and the theme is consistent. It's more difficult to overcome the challenges presented by flash manufactured at 25 nm than it was at 34 nm. But today's buyers should still expect better performance and reliability compared to previous-generation products. Succinctly, the lower number of program/erase cycles inherent to NAND cells created using smaller geometry continues to be overblown.


P/E Cycles
Total Terabytes Written (JEDEC formula)
Years till Write Exhaustion (10 GB/day, WA = 1.75)
25 nm, 80 GB SSD
3000
68.5 TBW
18.7 years
25 nm, 160 GB SSD
3000
137.1 TBW
37.5 years
34 nm, 80 GB SSD
5000
114.2 TBW
31.3 years
34 nm, 160 GB SSD
5000
228.5 TBW
62.6 years


You shouldn’t have to worry about the number of P/E cycles that your SSD can sustain. The previous generation of consumer-oriented SSDs used 3x nm MLC NAND generally rated for 5000 cycles. In other words, you could write to and then erase data 5000 times before the NAND cells started losing their ability to retain data. On an 80 GB drive, that translated into writing 114 TB before conceivably starting to experience the effects of write exhaustion. Considering that the average desktop user writes, at most, 10 GB a day, it would take about 31 years to completely wear the drive out. With 25 nm NAND, this figure drops down to 18 years. Of course, we're oversimplifying a complex calculation. Issues like write amplification, compression, and garbage collection can affect those estimates. But overall, there is no reason you should have to monitor write endurance like some sort of doomsday clock on your desktop.

Obviously, we know that SSDs still fail, though. All it takes is 10 minutes of flipping through customer reviews on Newegg's listings. But write-cycle exhaustion isn't the problem. Sometimes firmware is to blame. We know this because of the firmware updates vendors issue specifically targeting a documented problem. Other failures are electronic in nature. A capacitor or memory IC might go out, taking the SSD with it. Of course, we'd expect fewer issues with SSDs than hard drives, which have moving parts that invariably wear out over time. Do solid-state drives' lack of moving parts translate into higher reliability? Is the data on your SSD any safer than it would be on a hard drive?

With that question weighing on an increasing number of enthusiasts' and IT professionals' minds, we set out to investigate SSD reliability and sort the facts from the fiction.

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  • AlexIsAlex
    The 'drive completely dead, data unrecoverable' failure mode is not the worst; I can restore yesterday's image and lose, at most, a day's data (acceptable for my usage - obv. tailor backup frequency etc. to what's acceptable to you).

    The worst is what happened to my last SSD. For weeks I thought the problems I was seeing were software issues: the occasional crash, the odd SxS error in the event log, a game failing Steam file validation, an
    old email showing half garbled. Eventually, I managed to diagnose the problem.

    Old, untouched, files on the SSD were being corrupted at a very low rate (a few bytes per GB, I'd estimate). A file could be written and verified after writing, but days later might fail a checksum test when read. Without any error notification, SMART or otherwise, to indicate that the data read was anything other than perfect.

    Now that was a problem. Who knows when the last backup image without any corruption was? How can you even tell? The vast majority of files will be fine, but some will be backed up corrupt, and may have been for some time. With much manual effort I eventually did recover everything important, but my new backup regime involves checksumming everything on the SSD weekly. If something has changed data but not changed timestamp, this time I'm going to get some red flags!

    I can't say for certain that this failure mode is SSD specific, but it happened on my first SSD, and never on any of my spinners. Not enough data to be statistically significant, but enough to make me cautious.
  • Anonymous
    Can second the findings with regard to OCZ Vertex 2 drives. Mine has just gone and without any warning - all data lost after a year of light use. OCZ are completely useless in helping to fix it. It's like they know that their SSDs fail a lot and aren't at all surprised. Have gone onto Intel 320 SSD based on the hardware.fr findings.
  • dyvim
    Thanks Andrew, that's an interesting article even for a layman operating a single SSD ^^
    So far my OCZ Vertex 2 is doing fine, but then failure is always only a probability. System drives shouldn't be used to store important data in my eyes anyways.
    If not having mechanical parts doesn't really lower the percentage of dying drives, that only means that backup is just as important (and as often forgotten) as it always was.
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