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| SSD buyers guide |
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| the fastest SSDs |
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| the problem with
write IOPS in FSSDs |
storagesearch.com
by Zsolt Kerekes, editor
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| 11 years - "leading the way to the new storage frontier" |
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storagesearch.comby Zsolt Kerekes, editor |
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Can you trust flash SSD specs & benchmarks?published July 9, 2008 - we warned you first! |
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the SSD Buyers Guide flash SSD Jargon Explained Are MLC SSDs Safe in Enterprise Apps? the Problem with Write IOPS - in flash SSDs Data Integrity Challenges in flash SSD Design How Bad is - Choosing the Wrong SSD Supplier? Z's Laws - Predicting Future Flash SSD Performance Clarifying SSD Pricing - where does all the money go? Why Consumers Can Expect More Flaky Flash SSDs! Calling for an End to Unrealistic SSD vs HDD IOPS Comparisons the pros and cons of using ASAPs - (Auto-tuning SSD Accelerated Pools of storage) | ||||
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If you're a systems integrator
/ oem who has designed flash SSDs into a particular application - then it's
unlikely that you chose your favored models at random. It's much more likely
that you carefully evaluated products against a wish list of characteristics
which include:-
How can you be sure that the products which are going into your production systems are the same (or similar enough) to what you tested? It's possible that after you did all your qualification testing that the original SSD oem did some "improvements" which they may not necessarily tell you about - because they make the product "better". But what if the new SSD controller chip does work faster - but puts more stress on your limited battery budget? Or what if the SSD oem has switched suppliers of memory or power management chips and the overall product fails to operate reliably over the full range of temperature you need? Worse still - maybe you can't get the original product at all. To keep your production line going you have to stuff slots with products that your distributor suggests from companies you've never heard of before. Many of these problems have been around in the electrinics industry in past decades. But in 2008, 2009 and maybe 2010, the unique characteristics of the flash SSD market mean that the risks are a lot worse. Many SSD oems haven't been in the market very long. But because they make attractive products you can't afford to ignore them. Although some oems have been in the industrial or military markets for years - and do test their products and do inform you when those specs change - when their demand surges and products go on allocation - you still face the risks of switching suppliers to guarantee your own product's continuity. And here's another thing to worry about. Can you be sure - for example that the flash SSDs your buyer has bought at such a good price from an alternate source really are SLC? - and not MLC or SLC/hybrids. This is such a new market that you can't be sure that the supplier's SSD product manager (who may have been in the flash SSD business for less than 2 months) understands the intricate concerns you have - or what your questions mean. One solution to protect yourself - may be to do much more sample testing of incoming product. Or if your volumes aren't high enough to justify the capital expense - another option might be to ask your distributor to do the testing for you. The flash SSD market opens up tremendous opportunities for new products and systems which leverage that technology. But due to the diversity of products in the market and lack of industry standards - it's got tremendous risks as well. Paying proper attention to compliance testing and quality assurance will make the difference between the market success or failure of many new SSD based products. ...Later:- Sometimes the "specs" don't tell you anything meaningful about the product's performance at all - particularly in the case of write IOPS tests for flash SSDs. I've seen several published documents in which the measurements of such parameters appear to have been done incorrectly. Because there isn't widespread market experience of flash SSDs - it's easy to fall into the trap of running tests which were originally designed for hard disks or RAM SSDs and not realise that some of the inbuilt assumptions or test parameters may be inappropriate. It makes little or no difference to a small block size random write test on an HDD or RAM SSD whether the media being written to already contains data. The performance impact of fragmentation on HDD performance is well known. Flash SSDs don't suffer from a dropoff in performance due to fragmentation - but there can be a similar performance droppoff over time due to the lower availability of pre-erased blocks. So when benchmarking a new flash SSD (which is initially erased) it's important to take this factor into account. Some high performance lash SSDs have a background process which manages and tries to maximize the availability of pre-erased blocks. How well that works determines the sustained random write IOPS figure in 24x7 enterprise applications. That's why when testing a flash SSD for 24x7 enterprise applications you must make sure that when the benchmark window begins - the disk is already full. Otherwise you get a "halo" effect (similar to that caused by cache hits in traditional server benchmark tests) in which the pool of pre-erased flash storage makes the SSD "appear" to operate much faster than it will be in a real application after it has been running for days, weeks or months. About a year later:- STEC published this useful white paper - Benchmarking Enterprise SSDs (pdf). It reiterates many of the points originally raised in this StorageSearch.com article. |
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