It wasn't too long ago that many were decrying the 15,000 RPM HDD as dead, with the performance of the SSD being too much for the 15K HDDs to compete with. Unfortunately, for the SSD industry, this hasn't proven to be true. Currently SSDs consist of only 3% of enterprise storage capacity. 15K drives continue to thrive and grow in the datacenter.
Last year less than two million enterprise class SSDs shipped, compared to roughly 56 million enterprise HDDs. The enterprise HDD market is projected to grow 25% in units and 83% in total capacity this year alone. The data deluge has been brought on by the movement of data from the client to the cloud. This is partly due to the explosion of mobile computing, and the datacenter is in dire need of higher capacity storage devices that can also yield great performance.
SSDs will be an important component in the storage industry, but will do little to meet the demand for the Exabyte's of data required. Therefore, SSDs will continue to reside in the Enterprise HDDs shadow in terms of units shipped for the foreseeable future. The reality of the fact is that in the future SSDs and HDDs will both be prevalent in the datacenter, with tiered storage of data becoming more commonplace. Current data tiering strategies focus around three distinct layers, or 'tiers'.
Slower media in the bottom tier typically stores static data that isn't frequently accessed. This storage tier typically consists of tape and slower 7,200 RPM Nearline or SATA 3.5" HDDs. The middle tier of data storage holds more frequently accessed data stored on faster spinning media such as enterprise-class SAS 10,000 RPM HDDs.
The top tier is the 15,000-RPM SAS HDDs. This tier is all about speed of service, with only the most commonly accessed 'hot' data being stored on this more expensive tier of premium data storage. Estimates from many sources indicate that the 'hot' data in the majority of applications comprises less than 10% of the available storage pool.
More software caching solutions are becoming available that can intelligently identify and classify data. These solutions automatically move data between the tiers, optimizing the entire storage pool. The availability of these types of software tiering and caching solutions is growing, especially as SSDs gain more penetration into the datacenter. SSDs will begin to create a fourth tier for the most frequently accessed and modified data.
These tiers aren't rigid, and much of the segmentation will be decided by the type of workload and the application that is applied. Many of the standardized workloads listed above are actually well suited for high-performance HDD tiers. The workloads with high percentages of read activity, paired with low percentages of random writing, are particularly well suited for HDD usage.
The key takeaway is that HDDs are not displaced by SSDs, but merely another high performance layer will be introduced into the picture with SSDs residing in the top tier.