In an earlier post on “General vSphere Sizing,” I mentioned a storage IOPS calculator I had hacked together to help me with Vblock storage designs.  I used an earlier version of it to illustrate different scenarios in my post on “Application Sizing Assumptions.”  I’ve finally gotten around to posting the latest version and you can find it below in this post.  I hope that some folks will find it helpful.

Some quick instructions on how to access and to use the tool, followed by my design assumptions when I hacked the tool together:

The calculator can be directly accessed and used on this page and the formulas do work, although changes cannot be saved; since the entire calculator does not fit on the page, you can click on one of the buttons on the bottom right of the tool to display the full version on a separate web page.  Finally, you can use the button to download the actual calculator.

The IOPS calculator uses formulas based on the following application workload profile assumptions:

• Random I/O workload
• 8k block size

The assumptions above determine the operations per second, aka. back-end IOPS, for each drive type.  The ops/sec numbers for each drive tier in my calculator adheres to standard industry values but may vary from vendor to vendor; for an alternative method to calculate the ops/sec, I suggest reading Joshua Townsend’s post on “IOPS.”  The formulas in the calculator use ops/sec numbers, along with the values below to calculate storage IOPS, aka. RAID IOPS, for each RAID group:

• Quantity of drives per RAID group
• Read/write ratio
• Write penalty for each RAID type

The formulas in the calculator follow the format below:

Number of RAID Groups x (((Read Ratio x Disk Operations/Sec) + ((Write Ratio x Disk Operations/Sec)/Write Penalty)) x Quantity of Disk in RAID Group) = Storage IOPS

For example, for 15K SAS in a single RAID 10 (4+4) group, with 70% vs. 30% read/write ratio:

2 x (((70% x 180) + (30% x 180)/2)) x 8 = 2,448 IOPS

Please also note the following:

• The read/write ratio, number of RAID groups, and operations per second for each drive type can be modified to produce different results.
• The calculator is designed to allow IOPS to be calculated for the same or different RAID types and RAID group drive quantities.
• The write penalty is based on standard industry values; for more information on IOPS and RAID write penalties, I suggest reading Duncan Epping’s post on IOps in his blog, Yellow Bricks.
• The calculator does not factor in technologies such as caching and storage tiering.

Feedback and corrections are welcomed.  I hope this will be of value to you.

Related articles

• Application Sizing: It’s All About Your Assumptions (varchitectmusings.com)
• Back To Basics: General vSphere Sizing (varchitectmusings.com)