The devil is in the detail. Yes, I’d agree that using multiple SLC drives would probably be the best way to go for database servers today. I’d be mighty suspicious of the performance of MLC drives because of their slow random write speeds.

Ironically, when using SLC drives “life” of the equipment is not an issue … they will last a long, long time. So back to my original bent … make sure you know what you are purchasing when buying SSDs. There are many, many variables out there.

Ciao
Neil

I need to correct my previous calculations on SSD durability. A smart lady explained to me the concept of “write amplification” in SSDs. If the application writes a 8k block, the SSD controller must do an update of that 8k section of a much larger page. The page is the basic unit of the particular SSD that can be erased, sometimes called and ‘erase block’. So the controller reads the entire page, updates the 8k part, then erases and rewrites the full page. In effect, this 4k write has resulted in a much larger rewrite, hence the write amplification.

The effect depends on both the page size of the device and the average size of write commands. For database applications, 8k seems a realistic write size. Page sizes for current SSD are 128k or even larger. So the write amplification could well be 128/8=16. My previous calculated write endurance for the SSD drives of 1250 TB goes down to 78 TB and the life expectancy of 15 years becomes 11 month. But remember this was for a 100% write, 24×7 application. Under more realistic assumptions, this system would still run long enough to make replacement drives very cheap. So I maintain that it makes sense already to build database servers with internal SSDs in stead of 15k rpm drives or SAN connections.

Take care,
Ernst

I love reading your comments, because you obviously think about things before you just blunder down on paper (I must learn to do that sometime). You have extremely valid points, and I again point out that I love this technology and desperately want someone to give me a few of these things to try.

However … my issue is not so much with the technology, but with the way it’s marketed and sold. Is SSD the final answer? - No. Will it solve all problems? - No. Will it last very long in it’s current form - I seriously doubt it.

I was just reading over lunch about PCM (Phase Change Memory), which looks like it will have some serious impact on both memory and I think storage in years to come. This, and I’m sure many other examples of new technology, will mean that we keep moving forward with bigger, faster, smaller, lighter, cheaper (etc etc etc) storage devices.

As long as manufacturers tell us the truth, market their products in the right place, are upfront about both the strengths and weaknesses of their products and don’t hype it too much (in other words cut the b/s), then we don’t have too much to fear from what’s coming along.

Then again, without marketing teams I’d have nothing to write about.

Ciao
Neil

“Seeing an increase in failed SSD drives” brings the question … is this because they are failing more often than their platter counterparts or because there are more of them on the market to fail (than there was previously)?

We’ll never really know the failure rates of these devices. It’s not something that the manufacturers are ever going to tell us and if they did we’d have to take the numbers with a large dose of salt (lies, damned lies and statistics).

Just because something is faster does not necessarily make it better … just faster.

Ciao
Neil