Had a talk the other week with an storage executive about SSD and NAND cost trends. It seemed that everyone thought that $/GB for SSD was going to overtake (be less costly) than enterprise class disk sometime in 2013. But it appeared that NAND costs weren’t coming down as fast as anticipated and now this was going to take longer than expected.
A couple of other things are going on in the enterprise disk market that are also having an effect on the relative advantage of SSDs over disks. Probably, most concerning to SSD market is enterprise storage’s new penchant for sub-LUN tiering.
Automated sub-LUN storage tiering
The major storage vendors all currently support some form of automated storage tiering for SSD storage (NetApp’s Flash Cache does this differently but the impact on NAND storage requirements is arguably similar). Presumably, such tiering should take better advantage of any amount of SSD/NAND storage available to a storage system.
Prior to automated sub-LUN storage tiering, one had to move a whole LUN to SSDs to take advantage of its speed. However, I/O requests or access are not necessarily at the same intensity for all blocks of a LUN. So one would typically end up with an SSD LUN with a relatively few blocks being heavily accessed while the vast majority of its blocks would not be being hit that much. We paid the high price of SSD LUNs gladly to get the high performance for those few blocks that really needed it.
However, with sub-LUN tiering or NAND caching, one no longer has to move all the blocks of a LUN into NAND storage to gain its benefits. One can now just have the system identify those select blocks which need high performance and move those blocks and those blocks only to NAND storage. The net impact of sub-LUN tiering or NAND caching is that one should require less overall NAND storage to obtain the same performance as one had previously with SSDs alone.
On the other hand, some would say that making the performance advantages of NAND be available at a lower overall cost might actually increase the overall amount of NAND shipments. Also with automated sub-LUN tiering in place, this removes all the complexity needed previously to identify which LUNs needed higher performance. Reducing such complexity should increase SSD or NAND market penetration.
Nonetheless, I feel that given todays price differential of SSDs over enterprise disk, the people buying SSDs today have a very defined need for speed and would have paid the price anyways for SSD storage. Anything we do to make satisfying that need with less SSD or NAND storage should reduce the amount of SSDs shipped today.
But getting back to that price crossover point, as the relative price of NAND on $/GB comes down, having an easy way to take advantage of its better performance should increase its market adoption, even faster than price would do alone.