In this episode, the Radio Free HPC team looks at the Seven Myths of SSD vs. HDD Pricing, one of Henry’s recent Slashdotted features at Enterprise Storage Forum.
In a nutshell, Henry thinks that the notion of SSDs replacing spinning disks in the datacenter is built on several of flawed assumptions regarding flash storage.
- First, some assume that the price of MLC NAND flash will continue to decrease at a rapid and predictable rate that will make it competitive with HDDs for bandwidth, and nearly for capacity, by 2014 or 2015. This downward trend, it is assumed, will make flash a viable alternative for large storage and to act as a memory or “buffer” to improve performance.
- Second, there is a general assumption that prices for bandwidth ($/GB/s) for SSDs is much lower than for HDDs, and that enterprises will measure costs in these terms instead of capacity.
- Third, there is no distinction made between flash in general, such as consumer SSDs, and enterprise storage SSDs. It is assumed that MLC NAND will not only reduce in price ($/GB) but also that it will increase in density and larger capacity drives will be developed.
- Fourth, it is assumed that the quality of MLC NAND will either remain constant or increase as prices decrease and densities increase, allowing it to improve not only performance, but also reliability and power consumption of the systems it is used in.
- Fifth, it is assumed that power consumption for SSDs is, or will shortly be, significantly lower than that of HDDs overall, on a per GB basis and on a per GB/s basis.
- Sixth, they assume disk performance will grow at a constant rate of about 20 percent per generation and not improve.
- Seventh, they assume file system data layout will not improve to allow better disk utilization.
According to Henry, most of these assumptions were made in early 2012. So far they have turned out to be partially true at best and wrong at worst. A big fan of the partially true, Dan pushes back as a matter of principle. Rich, on the other hand, has heard his share of SSD hype and thinks we need need to look at the data and see what it has to say.
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