When Does Flash Storage Make Economic Sense?
In today’s world, IT organizations want everything to be better, faster, and cheaper. As changes come to the industry, it’s important to understand how to measure improvement. Specific to flash storage, it’s important to understand how choices about flash versus disk impact the bottom line. When it comes to making this determination, how can you be sure you’re getting the most out of every dollar?
Storage Cost Metrics
There are two primary ways to measure the cost of storage: it can be calculated in terms of performance or in terms of capacity.
Performance: Cost per IOPS
One way to measure the cost of storage is to calculate based on total IOPS performance in relation to size; this is called Cost per IOPS. As an example, if a PCIe SSD which costs $6,750 can deliver 200,000 IOPS, the $/IOPS would be about $0.03 per IOPS. By comparison, even a high-performing HDD like a 15K SAS disk of a comparable size would cost $180 and might deliver about 180 IOPS. This gives it a $/IOPS of $1/IOPS.
It is clear from the example that flash storage stands head and shoulders above spinning disks when it comes to economy in terms of performance. However, storage performance is but one factor in a storage decision. While flash storage is inexpensive in terms of performance, it still comes with a substantial cost it terms of capacity.
Capacity: Cost per GB
The other way storage cost is commonly measured is in terms of capacity in relation to cost. This number is called Cost per Gigabyte (GB). The same PCIe SSD used in the previous calculations costs $6,750 and has a raw capacity of 700 GB. This gives it a $/GB of $9.64/GB. The HDD costs $180 and has a capacity of 600 GB; so it comes in at $0.30/GB. Cost per GB generally drops substantially as the size of a spinning disk increases. For example, a 4 TB SATA disk costing $220 has a $/GB figure of just $0.05/GB.
Because organizations care about both performance and cost, and each medium is outstanding in only one metric, there must be a way to determine which is the right choice.
The Break-Even for Flash
By using a simple formula, you can begin to determine whether flash is more or less economical for any given purpose. This formula can be complicated by data reduction methods. Data reduction methods will be covered in-depth below. But at a raw capacity level, the economy of flash can be calculated this way:
IOPS required / GB required < cost per GB (SSD) / cost per IOPS (HDD)
Spinning disk as a medium is still substantially less expensive in terms of capacity than flash, but flash is much higher performing. To find the most economical choice, you must find the break-even point between the two factors. This is the purpose of the formula above.
When it costs more to produce enough performance with spinning disks than it costs to provide enough capacity with flash, flash is the most economical choice. A practical example using SharePoint as a workload could be calculated as follows: Microsoft documentation states that for SharePoint 2010, 2 IOPS/GB is preferred for performance. This calculation uses a SATA SSD rather than the PCIe SSD used in the previous calculation:
2 IOPS / GB > $1.96(GB/flash) / $1(IOPS/HDD) Answer: 2 > 1.96
This expression evaluates to “True,” which means that for this particular application, it would actually be slightly cheaper to use flash, and this expression has not yet accounted for any capacity optimizations (data reduction) of the flash storage. If more data can be squeezed into flash, it brings the break-even point even lower.
Learn how to:
- Find a balance of storage media that works for your business
- Establish a budget for your storage goals
- Select the right storage for your organization
- Use technologies like compression and deduplication to reduce your storage needs and improve performance