An update on the state of the SSD
Last summer, we brought you “A Brief History of Solid State Drives,” which outlined the evolution of the SSD through the ages.
Now that it’s a year later, we thought it fitting to revisit changes over the last year and give an updated look at the future of SSDs.
Long Term Studies
Until recently, there have been few long term studies focused on SSD behavior and characteristics. However, in this recently published study, Carnegie Mellon University and Facebook take the first large scale and long term look at answering many lingering questions about SSD performance and behavior in the data center.
Here are a few key insights from their report:
1. The failure profile of SSDs differ from HDDs. While HDDs are regarded to have a ‘bathtub graph’ of reliability where drive failures occur either immediately, or way down the road at the predicted end of their lifespan. However, the reliability graph for SSDs looks different, due to an early period of URE’s (Unrecoverable Read Errors) as faulty cells are detected and flagged. The self-monitoring serves to increase the overall reliability for the life of an SSD.
2. SSDs require a surprising amount of power to run. As power consumption increased, they found a correlation of increased failure rates.
3. Data stored sparsely across the physical drive can lead to higher failure rates.
4. Data writes cause significantly more wear on flash cells than reads. As a result, for write-intensive applications such as logging, HDDs may still be a better choice.
5. Higher operating temps were correlated with increased failures – more so than with HDDs. These failures can be mitigated by throttling, though early SSDs did not include this functionality.
Some of this information, such as drive wear from writes vs reads, have been know to us for some time. However, other information about temperature based failures and power consumption are very interesting insights.
Pogo’s three main takeaways:
1. SSD performance is still the number one selling point. Density, environmental conditions, and power consumption are secondary.
2. The number of writes per day matters. Matching an SSD wear level to a specific use case is important.
3. HDDs are not going away. Even with 3D NAND, ultra high capacity HDDs are still going to be the choice for archival storage. This is made even more relevant by the fact that if SSDs are left powered off for even a few months, they can begin to lose their data integrity.
With respect to players in the market, not much has changed. The wave of consolidation is over and three or four dominant brands remain in the market. With a few years now to perfect the technology, reliability has increased and performance is more consistent. There are also SATA and SAS options for almost any capacity and wear level that is desired. This has given consumers a lot of choice and driven down costs significantly.
Speaking of cost, how much have prices come down? This graph shows the downward pricing trends of two SSDs we commonly use in our configurations.
What does the future hold? The big news as we announced in our previous blog post, is the move to 3D NAND. This will provide a huge capacity increase over the existing technologies and should continue to reduce the overall price per GB. SSDs supporting 3D NAND should start shipping later Q4 to Q1 of next year. We are very excited about this development and can’t wait to see capacities in the 10’s of TB!
Last year around this time we also predicted the rise of the NVMe form factor to direct connect SSDs to the PCIe bus of a system. Turns out this form factor has taken much longer to catch on than we anticipated. We still believe that long term this will be the preferred method to attach SSDs to a system. It is very hard to continue to decrease latency in the I/O sub-system and this is the next logical step. However, there are still very few NVMe SSDs on the market, although most vendors say there will be many more options by the end of the year.
A lot has changed in the SSD market over the last year. Not only do we have a better idea about the long term behaviors of SSD drives, prices have dropped and capacities continue to rise. With the announcement of future drives supporting 3D NAND, HDDs will face even more competition. While we still see the need for large spinning disks for archival storage, SSDs are quickly becoming the default option for many applications. The coming year will continue to be an interesting time in the SSD market.
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