Overview

OneIQ uses standard VMware APIs to gather inventory and performance data. The VMware vSphere UI displays storage metrics in Terabytes (TB), not Tebibytes (TiB).

Here's an example from OneIQ lab that shows the VMware vSAN datastore and its capacity. As per the VMware vSphere UI, the capacity of the vSAN Datastore is 16.37 TB:

The capacity of the same datastore is 18TB in the OneIQ Portal when the TB metric is selected.

From the two screenshots, there is a difference of approximately 10%.

To understand why this is, we need to examine the API used by the vSphere UI: it shows "18003504660480" bytes.

If we convert 18003504660480 to TB and TiB it is

It turns out that vSphere Web UI shows the capacity in TiB, but represents it in TB.

This is because disk drive manufacturers tend to use the decimal system when labelling the capacity of physical disk drives. On the other hand, Operating System vendors prefer to use the binary system to measure computer memory and data storage capacity.

For example, it is quite common to buy a new physical drive labeled as 1TB and discover that when mounted to an OS, it has 931.32 gigabytes (GB) of capacity.

Providing optimal recommendations is one of our primary goals, and that's why we stress the importance of understanding the different metrics and systems.