Math for Storage Design: Part One – Performance

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In the past 15 years virtualization has transitioned from a novelty to the de facto standard for data center operation. Until recently few people understood the real implications of this transition, especially in the realm of storage.

We’ve seen servers go from almost all direct attached storage, to complex SAN and NAS arrays, and now back to direct attached with the trend in node based hyper-convergence technologies like VSAN.

No matter what you choose for your storage there are certain things you need to consider. Most folks plan for capacity, but throughput and performance are just as important. Here are some rough guides to help you with sizing your storage.

Performance, the IOPS Story

Input Output Operations per Second, or IOPS for short, is the main measurement of storage performance. Unfortunately IOPS can be co-opted by less than truthful marketing because all IOPS are not the same. The discussion of performance cannot be isolated to the driver or array. Workload matters. It is important to understand the percent of reads vs. writes, randomness of the drive access, and block size.

When researching storage options be cautious with vendor reported numbers. Most vendors report IOPS based on 4K random reads, your workload is most likely much different so be sure to test the hardware yourself to verify.

Formula for IOPS of a single non-SSD hard drive:

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