Further discussion from website at #5:
Are MLC SSDs Ever Safe in Enterprise Apps?
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SLC versus MLC in Enterprise SSD arrays - by Zsolt Kerekes, editor, June 2008
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The original purpose of my SSD Myths article was to show that you needn't worry about wear-out if you use "best of breed" flash SSDs with write-endurance on the order of 1 million cycles and above.
When it was first published (in March 2007) all flash SSDs in traditional hard disk form factors used SLC.
But in the year following publication many leading SSD oems (including Samsung, Mtron and STEC ) have also introduced MLC products too.
To confuse things even more - in June 2008 - Silicon Motion announced a new family of flash SSD controllers which enable oems to mix and match MLC and SLC chips in the same drive - creating in effect SLC-MLC hybrid SSDs.
MLC doubles the capacity of flash memory by interpreting 4 digital states in the signal stored in a single cell - instead of the traditional (binary) 2 digital states.
This technique has been commercialized and proven over many years in hundreds of millions of cell phones and MP3 / iPod music players - where the theoretical consequence of data corruption (if anything went wrong with this risky "new" storage technology) was no more serious than an inaudible sub millisecond sound blip or invisible pixel splat.
In the SSD market MLC yields much lower cost storage than SLC with read / write speeds which are nearly as fast as the best SLC devices.
The manufacturers of first generation "hard disk replacement" MLC flash SSDs have responsibly classified them as aimed at the "notebook market" and by subtle wording differentiated them from their more pricey "enterprise" products. In the low duty cycle world of a notebook these MLC SSDs should give a good operating life - typically similar to the hard disks they replace. (Most SSD marketers would claim their MTBFs are even better than HDDs).
But there's no way to tell the difference between SLC and MLC SSDs externally (apart from the model numbers). Put them in a rackmount system in a datacenter with fast processors which can pump them continuously close to the maximum speed and what happens? |