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The main advantage of SSD drives is better performance. I am interested in their reliability.

Are SSD drives more reliable then normal hard drives? Some people say they must be because they have no moving parts, but I am concerned about the fact that this is a new technology that is possibly not completely matured yet.

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up vote 33 down vote accepted

They haven't been around long enough in enough quantities to develop an earned reputation. Flash-wear is the really big one everyone is concerned about, which is why the enterprise SSD drives allocate so many blocks to the bad-block store. Anandtech has run several articles about SSD's over the last couple months and they go into a lot of detail. From what I've read, stability problems are primarily in the consumer market where corners are being cut to bring prices down out of orbit. The SSD's you can buy to put in your fibre channel arrays are a completely different class than the OCZ drives. There is perhaps a much larger stability divide between consumer grade SSD's and enterprise SSD's than there are in consumer SATA drives and enterprise SATA drives.

For more information about enterprise SSDs like the Intel X25, Anandtech has several article about that. Their introductory article about the X25 practically gushed. On the desktop side a recent article about the OCZ Vertex went into some detail about how bad the consumer side of the SSD market really was, and linked to another article where the problem was originally identified in the tech media. In short, consumer-grade SSDs were tweaked to provide massive sequential I/O numbers with little regard to actual usage patterns. The OCZ Vertex is a consumer-grade SSD that can approach the Intel for performance, but it requires babying to get there. Again, none of these have been on the market long enough for outright failure rates to really emerge. It has only been in the last, oh, 6-8 months that consumer SSD's have gotten cheap enough for mass adoption.


Update 6/2011

Two years later, and we do have some feelings for this now. However, how they're used has evolved. SSDs are used in areas where outright performance can't be economically met with disks, so comparing reliability is something of an apples-to-pears comparison. For servers that need small storage, they usually don't also need high performance on that storage so rotational magnetic media is still used most of the time.

That said, some comparisons can be drawn. SSD are typically used in large storage arrays as the highest tier of performance. In this role I've heard anecdotal reports that SSDs last a lot shorter than the same disks in those arrays. Like, on the order of 10-18 months. This is reflected in the warranty the big storage vendors allow on SSDs.

This may look like "a lot less reliable", but in reality you have to look at it right. Modern top tier SSDs can handle I/O Operations per second into the six digits these days, reaching the performance of even one drive with 15K RPM disks will take well over a hundred spindles. More mid-grade SSDs can do 30-50K I/O Ops, which is still over a hundred 15K disks. Modern disk I/O systems can't keep up with speeds like this, which is why the big array vendors only allow a few SSDs per array relative to disks; they simply can't eek enough performance out of the entire system to keep those things fed.

So in reality, we're comparing a brace of (for example) 8 mid-grade SSDs versus 250 15K drives. Since this is enterprise storage, give them an 80% duty cycle. In the first year a couple of those 15K drives will definitely fail requiring replacement, possibly up to 20. Anecdotaly, half of the SSDs will fail. When looked at it like this, failure rate for performance given, SSDs still aren't up to HDs. When looked at it from an economic point of view, each SSD is worth 31.25 HDs, SSDs are markedly cheaper for the performance given so the increased failure rate is more acceptable since replacement-rate is still probably cheaper in the long run.

Looking at it another way, a direct apples-to-apples comparison, where you subject the same two devices to identical I/O loads over a period of time, SSDs are more reliable these days. Take a 15K drive and a mid-grade SSD (50K I/O Ops/s) and give them both a steady diet of 180 I/O ops, and it is more likely that the SSD will make it to 5 years without fault than the HD. It's a statistical dance to be sure, but that's where things are going now.

Hard-drives still have the edge in the drive-unit failure rate per GB of storage provided. However, this is not a market segment that SSD are intended to be competitive.

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Thanks. The Anandtech article is very interesting. Interesting point regarding consumer vs. enterprise SSD's. Can you add links to discussions/ reviews about enterprise SSD's? I wasn't even aware they existed. –  Dani van der Meer May 29 '09 at 5:26
    
Very good update. It also meets my experiences. What people forget is that a crappy little mid range SSD replaces an array of high end discs IOPS wise. Heck, if I make a RAID 5 of 3 SSD... I still am ahead performance wise to a RAID 10 of a dozen discs ;) –  TomTom Jun 19 '11 at 5:20
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An average SSD is mature enough for everyday use, and depending on the use cases, could have a better lifespan than a traditional drive. In cases where a lot of physical abuse is likely -- lots of heat or vibration -- SSDs will generally be more reliable than a traditional mechanical drive.

It's up to you to balance the cost/benefit ratio, but I upgraded my 3 year old laptop with an SSD and the difference is absolutely amazing. I went with the Intel 80GB model for about $400. It is pricey, but not compared to the cost of a brand new laptop. The laptop feels brand new -- even though the processor and RAM are medium-range from 3 years ago, the hard disk was the bottleneck. Hard disks have been the biggest bottleneck in non-gaming computing for the past decade. They have become bigger but not much faster.

Using other people's laptops with their 5400rpm drives is pretty much unbearable now. Seconds feel like minutes while waiting for those ancient things to spin and churn.

Of course, you should always be backing up regularly, because mechanical drives are relatively likely to fail. With SSDs the importance of backing up is not diminished at all.

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Good point about the cost of SSD's vs laptops these days! –  sysadmin1138 May 29 '09 at 1:46
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see this link from codiing horror:

http://www.codinghorror.com/blog/2011/05/the-hot-crazy-solid-state-drive-scale.html

.." He purchased eight SSDs over the last two years … and all of them failed." "Solid state hard drives are so freaking amazing performance wise, and the experience you will have with them is so transformative, that I don't even care if they fail every 12 months on average! "

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For reliability in rough environments, any SSD is probably going to out-rate a normal hard drive.

We work for a building/plubming/painting company and all their employees have laptops in their cars. Tradies aren't known for being gentle with equipment, and the laptops get thrown around a lot. In this situation, any SSD is going to be great, because there's no moving parts and thus no heads to get stuck and scratch the buggery out of the drive when it gets dropped in the middle of booting up.

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An important thing to consider is the warranty, a typical enterprise SAS hard drive comes with a 5 year warranty. I have yet to see a SSD with a warranty over 1 year, this is probably due to the drives being relatively untested in production systems, it could also indicate the manufacturer believes that the drives are not as reliable as platter based disks.

This topic was recently discussed in an episode of .NET Rocks and they came to the conclusion that RAID based mirroring was probably the answer, as long as the disc is replaced quickly the data will always be protected from hardware failure.

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The better enterprise SSDs have comparable warranties---For example STEC's Zeus. The spec sheet lists the warranty as 5 years. See stec-inc.com/downloads/flash_datasheets/iopsdatasheet.pdf –  Keith Smith Jul 14 '09 at 2:09
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My experience is that SSDs have a much higher failure rate than hard drives, due to the immaturity of the technology, and immaturity of the products developed around the technology.

This has nothing to do with the expected failure of blocks. Between wear-leveling and spare blocks to handle failures, I've never seen a recent SSD that could start experiencing block failures within a three-year lifespan of nonstop writes. Either they're cheap and their write performance is too poor, or they're expensive and they have enough spare blocks.

If the drive is going to experience undue mechanical stress, I've seen SSDs experience much lower failure rates than hard drives. For example, in airplanes.

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Thanks for the interesting answer. Can you explain more your first paragraph? Or provide links to other documentats? –  Dani van der Meer Jun 4 '09 at 3:06
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Storage Search notes that modern flash memory is designed for typically one million writes, but if you are lucky may be good for up to 5x as many writes, depending on monitoring during manufacturing

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This artical (http://www.internetnews.com/storage/article.php/3801821/HP+Lays+Out+SSD+Datacenter+Ambitions.htm) reveals three main issues re the enterprise SSD.

  1. No hop-swap
  2. Slow write performance
  3. The capacity. While using MLC as the main type to increase the capacity, it reduces the native lifespan quite dramatically.

Unless these 3 issues are addressed, we won't see the SSD widely adopted in enterprise level.

Cheers.

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There are high-end SSDs that address all of these. The one I'm familiar with off the top of my head is the Zeus IOPS from STEC. It's a hot-swappable Fibre Channel drive built with SLC flash. Due to smart firmware and heavy over-provisioning of flash, it can do more than 10,000 write IOPS/sec. It's also rather price---several thousand dollars for a 256GB drive. While that may make it seem prohibitive, the theory is that enough traditional disks to deliver those IOPS would cost even more. –  Keith Smith Jul 14 '09 at 2:18
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Although SSDs haven't been around for that long, there are many companies such as Violin Memory Inc and Texas Memory Inc. producing scalable, fast and very reliable SSDs. It is worth to visit their web sites to learn more about the reliability of enterprise class SSDs.

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