Overview

OneIQ uses standard VMware APIs to gather inventory and performance data. During the testing of the VMware integration, it was discovered that VMware vSphere UI displays storage metrics in Tebibytes (TiB), not Terabytes (TB).

Here's an example from OneIQ lab, that shows VMWare vSAN datastore and its capacity. As per the VMware vSphere UI, the capacity of the vsanDatastore 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, it seems that there is a difference of approximately 10%.

To understand the reason for this, we need to drill down into 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 caused by the fact that disk drive manufacturers tend to use the decimal system when labelling the capacity of physical disk drives. On the other hand, the 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 labelled as 1TB and when mounting it to an OS discover it is 931.32 gigabytes (GB) of capacity.

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