Flash Data Storage: Myth vs. Reality

Posted on September 25, 2013 By Greg Schulz

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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



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