SSDs vs. Disks: Which Are More Reliable?

Robin Harris is an analyst who tracks emerging IT technologies and writes about the storage sector at Storage Mojo and Storage Bits.

Solid-state drives are often marketed as being more reliable than hard drives. But some evidence suggests that isn’t always true. How much more reliable than hard drives can SSD’s really be?

A retailer of SSDs and hard drives published its return data last month. Some of the 1 TB hard drives were more reliable than some of the SSDs. And when you consider the much larger number of bits on each hard drive, the per-bit reliability looks even better.

Why do hard drives fail?
Google’s study of hard drive failures – see Google’s disk failure experience and Everything you know about disks is wrong – found that 36 percent of failed hard drives did not exhibit a single SMART monitored failure.

Why? Because drive failures have two components: mechanical and electrical.

Hard drives are mechanical devices. Over time components wear: platters start wobbling; actuators lose precision; lubricants dry. The result: more retries; more corrupted data requiring ECC recovery: higher drive temperatures: greater power draw. These are the kinds of things that SMART records.

If SMART (Self-Monitoring, Analysis, and Reporting Technology) warns you of an impending drive failure, you should respond. But SMART is almost useless because of the failure modes it can’t predict. Power regulators, capacitors, traces, firmware and connectors can all cause hard drive failures. And SMART can’t warn about those.

What’s different with SSD’s
SSD’s replace the platters, heads, bearings and motors of a hard drive with flash. But they don’t replace the electrical components that cause many hard drive failures.

If all flash chips were the same, we could calculate how much more reliable an SSD should be. But they aren’t: manufacturers bin chips into different grades just as they do with CPUs. Manufacturers who build SSDs, such as Intel, Toshiba, and Samsung, often use the highest grade chips for their own SSD’s.

The lesser quality chips are sold on the open market. Most such chips go into USB drives and SD cards, but can go into SSDs – which probably explains the reported return rates for disk drives and SSDs. The high-quality SSD’ had fewer chip failures and the lower quality ones had more.

Fifteen years ago disk drives had significant differences in performance and quality. Today disk drives of given spec are much more similar.

SSDs today are where disk drives were 15 years ago: big differences – even from generation to generation within a single vendor’s line. The firmware layer that makes flash look like disk – the Flash Translation Layer – is evolving rapidly.

There is good news. Over the next year SSD prices will drop by 50%. Likewise, the quality of controllers and chip error detection and correction is rapidly improving.

Over a five year life I would expect an SSD to offer a 30%-40% lower annual failure rate than a mature disk drive. On the other hand, that disk drive will store considerably more information for lower cost. New, higher reliability drive technologies – such as HAMR and patterned media – are coming, but we’ll have to wait and see how good they are.

Given the trends, 2011 is the year even conservative data center managers will begin integrating SSD’s into their server infrastructure.

Comments welcome, of course. Thanks to Intel Fellow Neal Mielke and Application Engineer James Meyers for briefing me on quality issues. Conclusions are my own.

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  1. Of course not ALL SSD's will be more reliable than ALL standard hard disks, if that statement is a surprise to anyone, well, you're not that bright... In general, for what data centers use them for SSD's are more reliable than standard hard drives. Are they perfect, no. Compare enterprise SSD's like the Intel X25-E or similar to 15k RPM SAS drives and the reliability numbers are very, very good. Higher rotational speeds will often result in faster wearing, especially if it is a highly utilized device in a 24/7 enterprise environment. Also, why keep comparing the amount of data you can store on an SSD vs. on a standard hard drive? The reason for SSD's is IOs, not capacity. To reach the same number of IO/sec as a single high quality SSD you're going to need 16+ 15k RPM drives. Now, which is going to take less space, power, upfront cost, and maintenance, 16 drives + RAID card or 1 SSD?

  2. Kevin

    A great article! Why didn't the author point out that the Intel drives ARE delivering the reliabilty according to the article he refers to stating TB drives have better reliability thatn some SSDs. Why didn't he link that article? Going into that article it shows Intel drives have 50-75% better reliability than the most relialbe hard drives. The author explains it nicely later by explaining how some SSD makers use cheaper chips, but could have make the point much better by providing full context. All SSDs are not created equal and there are some out there that DO deliver on the reliability promise of solid state technology. Great point made by the commenter that SSDs are even MORE reliaible when looking at applications where one SSD replaces multiple hard drives. With the data Robin refers to (but didn't link) one can conclude that the right SSD is much more reliable than a hard drive TODAY.

  3. Mike H

    It is true that they are faster but I am not impressed with SSD. I am already on my 2nd SSD drive. I started using my 6 year old Maxtor HDD yesterday, will not spend another penny on SSD...

  4. Thnx . I was looking for this information

  5. Jim

    I have experienced much higher failure rates with SSD than platter based drives. I have had conventional hard drives fail, but usually its because I did something dumb, like drop it. The ones conventional drives I've installed and not dropped have pretty much never failed and my computers never get a rest. My SSD and flash devices have all failed and it doesn't seem to take much time for that to happen either. My feeiing on SSDs is that when it comes to consumer PC market, they are not ready for prime time.

  6. i have yet to see a ssd in my pc last longer then 11 months, whereas some pcs i use are still chugging away on mechanical drives that are a decade old. and the ssd's that i actually use for heavy workload all die with in a few days to a few weeks. the idea that ssd is more reliable than hard drive is the biggest urban myth i ever came across

  7. wizarddrummer

    In my opinion, Hard drives are less reliable than they were years ago. While the storage capacity has increased exponentially, the reliability factor has decreased. I have some older drives that don't hold much that STILL function as well as they did when they are new. I have two 500GB Western Digital (3 clicks of death) paper weights that died within a few months of each other and when I Google this it appears many other people have experienced this. These drives were only 3.5 years old when they died. I now have MAXTOR 152 GB SATA hard drive that starts to click at least once per day and freezes the computer sometimes twice per day. I turn off the machine and it comes up all right. This is an error that S.M.A.R.T. does not catch. I've even run the extended diagnostics on the drive and that didn't uncover anything either. I'm sick of disks that spin, at least these new generation of disks that are like throwaways but I don't have the cash to buy a new HD every year. This is why I was researching the reliability of SSD's I wish they'd worry less about HOW MUCH CAPACITY a drive has and more about HOW LONG WITHOUT PROBLEMS a drive will last.

  8. james braselton

    hi there wizzarddrummer you have failing hard drives lets 30 years 10 hard drive failuers i never use hard drive i use flash storage only or solid state drives not all were computers lets see i have 5 coputer hard drive failuers 2 dvrs hard drive failuers 2 hard drive camcorders hdd failuers a 250 gb xbox 360 failed soo and a 60 gb hard drive ipod failed useing macbook air 256 gb solid state drive 64 gb flash ipod a 4 gb ssd xbox 360 have a aptik i2 3d camcorder 4 gb sd card having hard drive failuers is not fun at all i will never go back too hard drives i dont want hard drives in millions of years

  9. Jack B. Dawson

    I've used nearly a dozen SSDs from different manufacturers, and had good luck with all of them. I have a couple of OCZ Octanes, an OCZ Vertex4, some Samsung 830s and 840s (the 840s are the Pro version), a Plextor and a couple Crucials. I also had an OCZ Vertex3 and a Patriot Pyro, although I sold them because they were only 64GB. Some folks have complained about SandForce-based SSDs but even my SandForce-based SSDs worked fine every time. Before last year, I was an SSD skeptic, but I'm much more of an SSD believer now. Of course, nothing beats having a solid backup strategy! One tool I would highly recommend is a tool called WindowSMART 2013. I run WindowSMART on all the computers in our home -- desktops and laptops, and it'll tell you the health of your hard drives and SSDs, even USB drives! It'll shoot you an email or an alert on your cell if disk troubles are detected. It even backs up the data off a disk that reports serious problems. It's been a few months, but I paid something like $25 for it and the license covers all your home PCs. Check out and look up WindowSMART. It comes as a 30 day trial so you can take it for a nice test drive. I say it was $25 well spent!