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Use cases for all-flash arrays
Traditional wisdom over the last few years has promoted the idea of tiering data across multiple layers of storage -- an approach that all-SSD arrays seem to contradict. However, the tiering methodology arose because storage arrays have grown and been used to serve general-purpose data. Solid-state arrays aren’t yet as highly scalable as traditional arrays, and it’s obvious that the relative expense of solid-state drives means all-flash arrays will be targeted at high IOPS applications rather than being used as general-purpose storage.
IOPS/$ and IOPS/GB
The traditional $/GB metric no longer applies for all-flash arrays; instead IOPS/$ and IOPS/GB are more effective measurements when comparing vendors. IOPS/$ indicates the cost effectiveness of the device when looking to get the best “bang for the buck” in high I/O environments. IOPS/GB indicates the relative I/O density of an array -- the ability to do as many reads and writes as possible per GB of storage.
We’re already seeing a division of SSD array vendors into those at the high end, delivering 500,000 to 1 million IOPS with sub-millisecond response times. These vendors include Kaminario, Texas Memory Systems, Violin Memory and Whiptail. Prices are typically around $15/GB to $20/GB.
Mainstream arrays from vendors such as Pure Storage and SolidFire Inc. deliver performance in the 100,000s of IOPS, with response times in the 1ms to 5ms range. Prices are lower than those of high-end products at approximately $5/GB to $10/GB.
The $/GB metric has been used for many years as a relative measure of array cost, especially as hard drive prices have eroded and drive capacities increased. However, $/GB isn’t a truly effective measurement when comparing high-end, all-flash arrays as the aim isn’t to deliver general-purpose, centralized storage but rather to meet specific application requirements. Where latency and IOPS are key, two measurements are more appropriate:
• IOPS/$, which measures “bang for the buck”
• IOPS/GB, which measures the I/O density of the storage array
Midrange vendors, such as Pure Storage and SolidFire, have chosen to implement data reduction techniques, such as compression and data deduplication, to increase the effective capacities of their SSD arrays and be in a position to compete on a more equal footing with traditional arrays in the $/GB battle. But not all data compresses equally; virtual server and virtual desktop data will compress well, but database data may not, so the $/GB figure quoted by these vendors may have to be taken as more of an indicator rather than an actual value.
No flash in the pan
All-flash storage arrays are a new class of product delivering high volumes of IOPS for demanding applications. We’re already seeing a segmentation of the market into mainstream and high-end products, based on IOPS and price. While not for everyone, all-flash arrays will find a niche in most enterprise environments.
BIO: Chris Evans is a UK-based storage consultant. He maintains The Storage Architect blog.
This was first published in August 2012