Making Flash Ready for Enterprise Primetime
by Hu Yoshida on Aug 23, 2012
Today, HDS is making an announcement about its strategy for incorporating flash technology across the IT stack. This includes a flash acceleration feature available today for Hitachi Virtual Storage Platform (VSP) that enables it to achieve more than 1,000,000+ random read IOPS.
Historically, the major inhibitor for the adoption of flash SSDs (solid-state drives) in the enterprise storage space has been the relative higher cost of SSDs versus HDDs (hard disk drives) and the durability of SSDs versus HDDs. These are two key inhibitors that need to be addressed before flash is ready for primetime in the enterprise space.
Most analysts are saying that the price erosion for HDDs have slowed to about 20% per year from the historical trend that was about 40% per year over the last 50 years. At the same time they are predicting that the price for MLC (multi-level cell) flash drives is declining by about 40% per year due to the increasing volumes driven in the consumer space for smart phones and other mobile devices. These volumes come at the expense of HDD volumes, which have used their volumes in the consumer space to offset the costs in the enterprise space. At this rate we can expect to see MLC flash become cheaper than performance optimized HDDs in the next 5 to 7 years.
However, price is not the only consideration when it comes to using HDDs or MLC flash in the enterprise space. There is a big difference in durability requirements for storage media that is used for a smart phone, which an individual can live without for an hour or two and trades in every two or three years; versus an enterprise storage unit that may be required to support hundreds or thousands of I/O operations on a daily basis and can never be down in 5 or more years. So durability is a major concern for enterprise use. Flash vendors are addressing the durability of flash drives with wear leveling, and aggressive sparing within the drive and may specify a 5-year life but only under certain conditions (e.g.no more than 10 times the capacity of the drive written per day). Enterprise storage cannot be limited to such conditions so the enterprise control unit must add additional durability and preemptive maintenance features to raise flash SSD endurance levels to the level of HDDs.
Another concern is performance, especially when many users must share the SSD across an external shared bus controller in an enterprise system versus an SSD that is dedicated to a single user over an internal connection, as you would find in consumer products like a smart phone. While the SSD is much faster than a mechanical HDD, bottlenecks can occur within the drive as writes/formats increase and space becomes fragmented. Bottlenecks also occur in traditional enterprise controllers, which were designed for mechanical spinning disks and may not be prepared to handle the transfer speeds of an SSD. In order to get the optimum performance from SSDs, the enterprise storage controller must be enhanced for SSDs while maintaining all the functionality that has been developed over the years. In other words we must avoid the rip and replace of current storage controllers to implement the improvements that are required to realize the performance benefits of an SSD.
HDS believes that flash is ready for enterprise prime time where random performance is a key requirement. The current price gap between flash SSDs and HDDs can be reduced with the use of MLC flash, which has 2 bits per cell versus one for SLC (single-level cell) flash. This reduces the cost per bit by about 30%. Features like HDT (Hitachi Dynamic Tiering) can optimize the use of flash by moving only the hot pages of a volume into a flash tier while the cold pages migrate down to lower cost HDD tiers. In addition, HDP (Hitachi Dynamic Provisioning) increases durability by providing global wear leveling, which supplements the wear leveling within the drives to avoid hotspots.
The flash acceleration feature announced today for VSP raises its scalability limits by up to 3 times, doubles the scalability of HDP, increases virtual storage director (VSD) random I/O throughput and lowers I/O response times by up to 65%. Flash device throughput is increased with higher thread count scalability. With more than 24 threads running against an all SSDs configuration we have measured 1,000,000+ IOPs using 8K random reads.
This flash acceleration feature comes with a microcode upgrade to V04A. Below are measured results for 100% reads with all MLC SSD drives. The results will vary with the RAID configuration, especially for writes.
Overall, the total maximum throughput of VSP with V04A and flash acceleration will exceed 1,000,000 IOPS.
This feature is available today with VSP microcode V04A for open systems. There is a small charge for this feature and the performance gains that are described here may not be realized in your current workload environment if you are not experiencing any bottlenecks with your VSP controller. Therefore this feature is provided with a 120 day free trial.
If you are considering the use of flash drives, this enhanced performance combined with the price of MLC flash from HDS makes the use of flash more affordable than previous SLC flash configurations. Here is a comparison of relative costs for SLC versus MLC versus MLC plus flash acceleration.
Flash media costs are coming down, but we don’t have to wait 5 to 7 years to enjoy the benefits of flash performance and environmentals. The cost of MLC flash along with the performance acceleration of flash acceleration on VSP brings the cost down dramatically compared to previous SLC flash offerings, making flash media affordable on all VSP configurations. The wear leveling capabilities of HDP and HDT, combined with RAID protection and preemptive sparing available with VSP, can assure the durability of MLC flash for prime time. Look for additional flash enhancements from Hitachi Data Systems in the near future.