Live Optics | Optical Prime | VM Whitespace and Negative Whitespace Values
Summary: Live Optics Virtual Machine (VM) Whitespace and Negative Whitespace Values
Instructions
VM Whitespace is the opposite but related value to VM Occupancy.
VM Whitespace = 100% - VM Occupancy %
If a VM is 33% Occupied, then the VM contains 67% Whitespace; 100% - 33% = 67%.
Understanding Negative Whitespace values
Less common but totally plausible, it is entirely possible to get a valid negative Whitespace value! And it is important that you know why. It is likely not an error.
Guest iSCSI connections will often produce negative whitespace values. The Guest iSCSI technique is fading in popularity, but it is wildly misunderstood as a VMware RDM. However, they are not the same.
What is the difference?
A RDM is a disk that is created and known to VMware. It is passed to the Guest OS by VMware. The bottom line is that VMware is aware of it.
A Guest iSCSI Disk is when the Guest OS uses its Microsoft/Linux guest iSCSI initiator to mount external storage directly. They key here is that VMware has NO knowledge or management of that capacity. The exception to this is that VMTools sees this capacity because it is installed in the guest OS and talking directly to the disk management services.
The net result is that it is entirely possible for a VM to report its capacity as much higher than the Virtual Disk Capacity numbers suggest is physically possible…and those higher numbers will likely be correct.
Example:
This Virtual Machine has mounted a 500TIB Guest iSCSI volume. This creates a 1-to-1 relationship between the Guest VM OS and the external storage provider. However, the VM is only using 325GIBs of the 500GIBs allocated.
In this situation, the 325GIBs is real capacity managed by the VM and needs to be considered, or capacity would be undersized.
|
Virtual Disk Capacity |
100GIBs |
vCenter VM size limitation |
|
Virtual Disk Used |
75GIBs |
vCenter VM measured size |
|
Guest VM Disk Capacity |
500GIBs |
OS measured capacity limitation |
|
Guest VM Disk Used |
325GIBs |
OS measured capacity used |
In this scenario 325GBs/75GBs = 4.33 leading to a 433% VMware VM Occupancy.
Whitespace is now naturally negative! Or 100% - 433% = -333% Whitepsace.
In Live Optics if you encounter any VM Occupancy greater than 100%, you will see the Guest iSCSI technique value set to True.
If an environment uses this technique aggressively then the average VM characteristics can show a negative number. When examining the Virtual Machines of any environment with a negative whitespace value be sure to look at the VM Occupancy column. There is likely many VMs with a VM Occupancy greater than 100%.
Simply put, this means that the environment has a lot more data managed by the VMs than VMware is reporting.