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Price of Flash and HDD

by Hu Yoshida on Apr 12, 2013

There is a lot of speculation about when the price of flash media will be on parity with hard disks. Several years ago, the projection was that lower cost MLC flash SSDs would cross over the SAS HDD price curve by 2019. This cross over point has been coming down rapidly as the volumes of flash SSDs have increased primarily at the expense of HDD volumes. (Remember when all PCs and even iPods had HDDs?) Last year some analysts projected that the cross over point would be reached in 2017, and more recently they are projecting sometime this year. This is for the general SSD market, which is not the same as the enterprise storage market. The cross over point for the enterprise storage market will be further out due to the performance and durability requirements for enterprise storage.

Today SSDs for enterprise storage are about 8 times the price of HDDs. Hitachi Data Systems designed their own controller for flash, which enables an individual Hitachi Flash Module to have 4 times the performance of a current MLC flash SSD, with 40% lower overall capacity costs through much larger capacity flash modules. With the upcoming availability of our 3.2TB Hitachi Accelerated Flash module, we can provide 614TB of raw capacity as a tier of storage within our Hitachi Virtual Storage Platform (VSP). On a per bit basis the 3.2TB Hitachi Accelerated Flash module is less than 4 times the price of high performance 15K 146GB HDDs. This Hitachi Accelerated Flash module will enable us to ride the eroding price curve of FLASH DIMM memory modules so that we should be close to parity with high performance HDDs by 2015. Because it will be a tier in the VSP, it will have all the functions of enterprise storage such as tiering, clones, snaps, replication, monitoring and management.

However, this does not mean that HDDs will go away. HDDs will still be able to provide larger capacities at lower cost. If it is used with flash in a dynamic tier of pooled resources, HDDs will be able to concentrate on increasing capacity without having to be so concerned about performance. While the technologies for increasing bit densities have slowed down, there are other ways to increase capacity such as through packaging as it was done with near line SAS. However, the future for high performance 15K RPM HDDs is not bright.

HDDs have another characteristic, which will ensure their continued use: durability. HDDs are approximately 1015 to 1016 while MLC flash is 103 to 104, in terms of re-writability. While Hitachi has extended the operational life of flash in the Hitachi Accelerated Flash module by reducing the amount of writes and formats. (See my post on how Hitachi addresses durability in Hitachi Accelerated Flash.) That operational life is about 5 years with unlimited write/formats. While this is an improvement over SSDs, it still does not compare with the durability of HDDs. This is another reason to use flash and HDDs in a dynamic pool, so that the bulk of the data resides on large capacity HDDs over a longer period while the smaller set of active data resides on flash, which will need to be refreshed on a shorter cycle.

While there are other technologies for non-volatile memory it will take some time for them to displace flash in the volumes that will make their prices competitive. So while we will see parity in the price of flash storage modules and HDDs in the next few years, we will continue to see combinations of flash and HDDs in dynamic tiers of storage.

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