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The VMware Cloud on AWS service is a bridge between two worlds in more ways than one. The Service connects traditional on-premises infrastructure to modern cloud environments. For the most part, VMware Cloud has obfuscated any differences successfully. One place where there are visible exceptions is storage capacity reporting.

What changed?

While vCenter Server continues to report storage capacity using SI prefixes, the VMware Cloud Services Console has transitioned to using the IEC International Standard prefixes.

I’m sorry, what?

If this is all gibberish to you, fear not. You’re not alone. You may have seen the familiar abbreviations MB, GB, TB. We use these labels throughout most VMware products because our products predate the IEC standard and our customers prefer the traditional prefixes. They are, however, incorrect.

Why the difference?

To answer that question, we’ll first ask another. How many bytes are in a TB?

A = 1,000,000,000,000 bytes

B = 1,099,511,627,776 bytes

It turns out your answer to that question depends on many factors because its meaning has changed over time. Within VMware, the correct answer is B, vCenter continues to use the TB prefix on a base-2 calculation. I.E. 1TB= 1,099,511,627,776 bytes.

Who cares, right? Is it just a label? .. Well, some of you answered A to our question.

TiB vs. TB

While the Terabyte is a standard unit of measurement, the definition changed over time—the computer industry, at its inception, borrowed standard unit notation as shorthand for memory notation. The familiar kilobytemegabyte, and gigabyte, and their corresponding symbols KB, MB, and GB became standard measurement units within the field. Most operating systems borrowed from the decimal system using SI prefixes on base-2 calculations for memory and storage capacity. Simultaneously, the hard drive manufacturers themselves used the decimal measurement assigning the same SI prefix.

This produced a perfect storm of confusion. A customer would purchase a 1TB hard drive to discover it was only 931GB in the guest. After several lawsuits, the industry developed several ways of dealing with this confusion. Some operating systems switched filesystems to use SI decimal notation and measurement.  Others moved to the new IEC binary notation (KiB, MiB, GiB, TiB, etc.). Microsoft has continued to use the SI prefix to refer to binary measurements.

With supported guest operating system vendors moving one way or another, there is no clear mandate. This inconsistency proved to be material because as scale increased the seemingly small difference between the two compounds to the point where it can make an enormous difference. Simultaneously, the VMware Cloud on AWS Service does have a requirement to deliver nonambiguous terms when deploying a vSphere Cluster. Therefore, we transitioned the VMware Cloud on AWS console to use IEC binary notation.

You may notice the numbers themselves have not changed. VMware has always calculated storage capacity using base-2.

Summary

Within the VMware Cloud on AWS console, all storage capacities are reported using IEC notation.

1TiB = 1,024 GiB = 1,048,576 MiB = 1,073,741,824 KiB = 1,099,511,627,776 bytes

vCenter Server continues to use SI prefixes for the same calculations.

1TB = 1,024 GB = 1,048,576 MB = 1,073,741,824 KB = 1,099,511,627,776 bytes

As of this writing, there are no plans to change vCenter as it continues to straddle the line with conflicting guest implementations. We hope this clears up why the unit label changed while the reported capacity has not.

 

Availability

To view the latest status of features for VMware Cloud on AWS, visit https://cloud.vmware.com/vmc-aws/roadmap.

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