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In the spin of SSDs on database servers

The future is static

Internet Security Threat Report 2014

SSDs can be thought of as a hybrid between rotating media and volatile memory and their adoption should significantly change intelligent indexing behavior. At its broadest this simply means that good DBAs will use fewer indexes. Also, the use of SSDs will almost certainly affect decisions about the placement of indexes: for example there may be far less of a performance hit from keeping data and indexes on the same device because SSDs are essentially random access.

Ingres and Postgres creator Michael Stonebraker is well known for his controversial opinion of MapReduce and he has also voiced strong views on row- and column-oriented databases. In transactional systems we tend to read most of the data in a row and in analytical systems we tend to read most of the contents of a column - somewhat of a simplification, but essentially true.

Stonebraker's argument is that in analytical databases we should store the data column-by-column so that the data most likely to be read together is stored together. It's a perfectly reasonable argument when discussing an HDD and - whilst I'm not suggesting that the argument evaporates completely with random access storage - I am saying that the use of SSDs will materially alter the balance here. In other words, for many systems it simply may not matter whether we use column or row-oriented storage.

Clearly SSDs are going to be seen in wider deployment on general purpose servers. And, just as we’ve developed ways of extracting the best from rotating media, we must now engage upon doing the same for solid state drives.

Then once we've grasped the idea that storage need not rotate, alternatives to SSDs also enter the picture. Why not oscillate instead? DataSlide, for example, is developing a Hard Rectangular Drive (HRD) with a "massively parallel 2D array of magnetic heads" past which the media moves. All sorts of good vibrations surround this device.

Bootnote: SSD explained

An SSD is a block of memory acting as a storage medium (meaning, incidentally, that the D in SSD is a misnomer as there's nothing physically disk-like about an SSD). The latest models, like Intel's X25-M, use NAND flash memory technology, which doesn't use power to maintain stored data. NAND is short for 'Not AND', a Boolean logic operator that describes how data is stored: its use in SSDs was pioneered by Samsung.

There are two flavors of NAND flash: single-level cell (SLC) which stores one bit per cell and multi-level cell (MLC) that - you guessed it - stores two. Both can be read very rapidly but writing to SLC is around twice as fast as writing to MLC.

On the other hand, MLC technology is cheaper: the 80Gb X25-M is MLC and the new bulk purchase price - 1,000 units - is $225, which works out at under $3 per gigabyte. One SLC Intel 32Gb X25-E costs around $350 or $11-ish per gig which, whilst not directly comparable for several reasons, at least gives a feel for the price differential. ®

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