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Analyzing Long-Term SSD Failure Rates
wintertargeter writes "It looks like Tom's Hardware has posted the first long-term study of SSD failure rates. The chart on the last page is interesting — based on numbers, it seems SSDs aren't more reliable than hard drives. "
I didn't read TFA but the chart doesn't tell me that "SSDs aren't more reliable than hard drives".. the SSDs were generally 6% or under (assuming the linear progression) whereas regular HDD approached 14%+ after five years. And "Long-term" in the title? The SSD data in the chart only goes for 1 year. Not exactly long term when the chart goes from 1-5 years of use. The actual data for the SSDs is only 20% of the time span.
Did the poster even look at the chart he linked to?
Did you? Apparently not.
Ignore the dashed lines-- those curves are not data, they are "projection." The chart has no data on SSD failures late in the lifetime. So, when you say "...SSD failures only exceed HD failures very early on in their lifetimes," that is equivalent to saying "SSD failures only exceed HD failures in the region of the graph for which there is data."
http://www.geoffreylandis.com
I remember there being lots of claims that SSDs would be more reliable because they had no moving parts.
The truth is that all men having power ought to be mistrusted. James Madison
Look closer. At any points where they have actual data, the failure rate for SSDs is higher than that of HDD, except for the Google study, which I bet puts the drives under massive load or something else funky (given its massive difference from all the other HDD charts.) Only in the projections for the SSDs do the HDDs begin to curve upwards, throwing off the graph. And from what I know of flash memory, especially MLC (which most SSDs are), I'd bet that SSDs will curve upwards too. Sure, wear leveling will help, but if a cell fails with data in it, which can still happen, then that data is lost. So yeah, for any section where they have actual data, SSDs do have a higher failure rate that hard drives. Incidentally, that's a really terrible and deceptive chart.
"None can love freedom heartily, but good men; the rest love not freedom, but license." --John Milton
Let me summarize:
A) Chart is worthless. I have never see a more ambiguous meaningless chart in my life. They might as well not bother to label things.
B) Lets do a reliability study on SSD's that they don't have any long term data on past 2 years, yet compare it to HDD that typically at least have a 3 year warranty. By that I only mean, I'll go out on a limb and guess that the average failure rate of HDD is > 3 years, if only for economic self preservation.
C) Results in either case depend highly on specific device model and configuration.
You do know that HDDs also require wear leveling right? (Well, not really, but defective blocks were pretty much part of life when HDDs were in the 10-100MB size.)
So yes, both SSDs and HDDs are likeyly to wear out after time. What wear leveling does is that it makes sure that the entire disk is pretty much worn out when you start encountering bad blocks.
With SSDs there is however one slight improvement. Since flash memory have been used for so long without wear leveling and in applications were it's damn important to get a good estimate of the the product life (Advanced fire alarms, mars probes and such.) it is actually possible to get good information on when a SSD is likely to fail.
I assume that HDD manufacturers have at least some clue of how many writes their disks will take before it is worn out (Otherwise they will have to alocate unused blocks for the wear leveling on a hunch.) but good luck getting that information from them.
So yes, both SSDs and HDDs are likely to fail sometime. The big difference is that if you are designing a system where it actually matters you can actually select an SSD with the correct specification. If it really matters you are probably going to get SLC anyway. If you don't want to pay for it it is likely that you don't need reliability.