Flash Data Storage: Myth vs. Reality

Forget the hype: here’s the truth about some common NAND flash SSD myths, from a technical perspective.

The interest in flash and SSD is huge – and so is the hype. So here’s the truth about some common nand flash SSD myths and realities to help you cut through the hype.

Feel free to add your perspectives in the Comment section below – and tell us about your favorite myth, fud and reality.

Myth: USB thumb drives are not SSD

Reality: That depends on your definition of what is or is not a SSD. On an enterprise storage system basis, a nand flash USB thumb drive is not on the level of that category of SSD solutions. However, for many other environments, a USB thumb drive is a SSD, just without all the feature, functionality and capabilities of a larger solution.

Myth: SSD are DRAM and not nand flash-based

Reality: This is a carry-over myth from those who first used DRAM based SSDs a few decades ago and now associated nand flash with USB thumb drives. The reality is that there are both DRAM and nand flash-based SSDs and even hybrid solutions that combine the two, not to mention Solid State Hybrid Disk that include DRAM, nand flash and a HDD.

Myth: You need software to leverage SSD

Reality: Some products, devices or solutions may require some software ranging from a driver, tiering or caching tool for management while others will be plug and play. For the plug and play type devices or systems, additional benefit can be derived from using value added software tools.

Myth: SSD is too expensive

Reality: One of the most common mistakes I see people make is looking at SSD in general on a cost per capacity basis vs. on a cost per activity basis.

Instead of looking at how much space capacity you get per cost, look at how much activity in terms of IOPs, bandwidth, files moved or accessed, work done or productivity enhanced per cost.

Doing so will show that for active environments where you can leverage the improved performance and lower response time, SSD will be less costly than many disk-based approaches. On the other hand, if you are not able to use or take advantage of that extra performance, then there may not be a benefit.

Myth: SSD only works in new systems or architectures

Reality: Some existing storage systems or appliances do a better job of taking advantage of supporting SSD vs. others. With some systems, there is more write optimization for performance as well as wear leveling to increase duty cycle, minimize program/erase (P/E) cycles vs. other solutions.

In some cases, I have seen where simply attaching an SSD to a vendor’s solution can have the same or lower performance vs. other vendors HDD-based solutions, yet for other products, there can be noticeable improvements.

Simply being able to support a SSD device (drive or card) is one thing, yet it’s another to be able to leverage it, integrate the device and optimize to coexist with RAID or other functions without introducing new problems. By the way, care to guess who wants the myth that SSD does not work with existing storage systems to exist?

Yes, the startups, particularly the all-SSD based ones. However, given that there are tens if not hundreds of PBytes of nand flash drives shipped, installed and in use with existing storage systems, I would say myth busted, with caveats of course.

Myth: Small IOs or IOPS are best for SSD?

Reality: For out of this world marketing metrics, the smaller the IOP the better. However, those may not be meaningful without context. On the other hand some SSD implementations are optimized for read or write bandwidth, thus not all solutions are the same.

Myth: Nand flash SSD are about to be replaced by PCM or MRAM or something new

Reality: In terms of talking about something new or different, sure, that is always the case. Some new things are in the labs or early qualification testing. However, also keep in mind that nand flash has yet to reach its full market potential in terms of industry deploy or customer adoption after over 20 years of existence as a technology. It’s safe to say that while there are new things to talk and get excited about, like the disk drive and other things, nand flash will be around for a while.

Myth: SSD is persistent so you do not need to protect with RAID mirroring or backup

Reality: Unless you are storing a copy of data that you will not ever need, make sure the data is protected just as you would if storing data on disk. This means for availability and accessibility using mirroring, replication or some other RAID variation, as well as versioning or time interval protection such as snapshots or copies.

Does that mean you cannot use nand flash SSD as a backup or archive target? You can use it as a backup or archive target just as disk or tape, however, if it is important then have another copy as you would. That’s part of a best practice.

Myth: RAID is not good for SSD

Reality: As with most anything, if you use it in the wrong way, or it is not a good implementation, things can break or wear out. This is true with some RAID implementations that cause extra writes to occur and thus write amplification that results in increased wear (P/E cycles) or shortened life of nand flash. On the other hand, there are good implementations that do not cause the extra writes to occur by leveraging caching, write gathering and other techniques. Thus, it depends.

Myth: Nand flash SSD are not reliable

Reality: In general, they are reliable and safe, yet with the caveats that not all are the same, nor are their implementation, so do your homework. Also, keep in mind that nand flash will wear out over time. However, some solutions today do a better job vs. others in optimizing duty cycle and minimizing wear.

Myth: Nand flash SSD wear out to fast

Reality: If you are doing 100% writes to a nand flash device that is very small, and that has no DRAM-based write caching or other write gathering and optimization, along with no other wear leveling, the device will wear out sooner vs. later.

However, if sized appropriately, with the right wear leveling and duty cycle optimization among other techniques, even in a heavy write environment you should be able to get a couple (or not many) years of use out of the device.

Myth: Nand flash SSDs will shrink in terms of space capacity over time.

Reality: the amount of free or usable space capacity naturally, just like a disk drive, will decrease as it gets used, then free up as items are removed. However, the stated space capacity of an SSD drive, just like a HDD, should not ever reduce over time other than space being used. Note that, like HDDs, there are spare or hidden capacity for handling errors, bad blocks and pages.

Myth: Nand flash SSDs will slow down as they fill up

Reality: This may happen from the operating system or storage solution as a volume gets fuller, however performance should not drop as the device fills up. On the other hand, over time (a long time) as the cells get worn out and the device is nearing the end of its useful life, it is possible some writes might take longer as things get moved around. But, based on implementation, that too might be a myth.

Are there even more nand flash SSD myths and realities than those mentioned?

Yes, including the one that says nand flash a SSD does not wear out like HDDs, or SSD needs to be in the server, or that SAS and SATA are too slow because they use legacy cylinder head sector addressing (reality is they use logical block addressing or LAB) among others.

About the author

Greg Schulz is Founder and Sr. Analyst of independent IT advisory and consultancy firm Server and StorageIO (StorageIO). He has worked in IT at an electrical utility, financial services and transportation firms in roles ranging from business applications development to systems management and architecture planning. Mr. Schulz is author of the Intel Recommended Reading List books “Cloud and Virtual Data Storage Networking” and “The Green and Virtual Data Center” via CRC Press and “Resilient Storage Neworks” (Elsevier) and a four time VMware vExpert. Learn more at www.storageio.com