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Nimble OS 2.1 : Part 10 VAAI Thin Provision Stun / Volume Online Non-Writable


Hello all & welcome to this blog again. This time I will talk about Thin Provision Stun Primitive

This feature expands Nimble's hypervisor integration by supporting the "Thin Provisioning Stun" primitive. Thin provisioning stun addresses the concern regarding the impact on virtual machines when thin-provisioned datastore usage reaches 100% of capacity.

Virtual machines running on hypervisors do not have a way to determine how much space a thin-provisioned datastore is consuming on the backend. The "Thin Provisioning Stun" primitive provides a mechanism by which the array is able to return warnings/errors to the hypervisor when specific space thresholds are exceeded for such datastores. In the absence of supporting this primitive, hypervisors had much more severe impact to their virtual machines when a datastore reached 100% of the capacity. For example, prior to vSphere 5.0, if a thin-provisioned datastore reaches 100 percent usage, no more virtual machines could be provisioned and other virtual machines stopped running. Ouch ! Starting in vSphere 5.0 (which supports this primitive), only those virtual machines that require extra blocks of storage space are paused; those not needing additional space continue to run.

To check if your VMware environment is using VAAI do the following :

Click Home > Demolab > Configuration > Storage. In the right hand pane under Datastores you will see some datastores


To check if VAAI is disabled of enabled click Advanced Settings under Software.


In the left hand pane click DataMover. If the value for DataMover.HardwareAccelleratedMove is 1 VAAI is enabled, if it is 0, VAAI is disabled on the ESX host.

Another way to check this is via the CLI


Now lets look what happens with the new supported Thin Provisioned Stun primitive on a Nimble array.

There are 2 Notifications available

1. Thin Provisioning Space Threshold Warning
This is a warning to alert the administrator if volume’s space usage exceeds a certain threshold = Soft Error
The administrator can proactively add more storage to this volume to avoid 100% quota

2. Thin Provisioning Stun/ Permanent Resource Exhaustion
When volume usage reaches 100% quota, all incoming writes would be failed with a check condition = Hard Error

Okay, lets look at the first notification :

1. Thin Provisioning Space Threshold Warning : First of all you can set a warning per volume level when your volume is running out of free space. This is done at creation of the volume:


In the example above you can see that a warning will be send if the volume overruns 80%. If the volume overrun this warning level the administrator can add more storage to this volume to avoid troubles. However before the administrator does this he will a message like this in ESX 5.1 :


2. Thin Provisioning Stun/ Permanent Resource Exhaustion

An additional setting is available in the performance policy. You can choose to go into “Online : Non-writable” or “Offline” mode on quota exhaustion:


If you discard the warning and fill the volume to 100% the following will happen :

The Nimble volume gets into a state “Online : Non-writable”. All the incoming writes are failed with a hard error. Windows and VAAI will handle this differently, lets focus on VAAI first.

  A. On reaching 100% volume quota, virtual machines on this volume requiring extra blocks of storage space are paused. All the other virtual machines continue to run



What do you see on the array when a volume goes into “Online : Non-writable” state?


An administrator will have to do the following when the volume goes into “Online : Non-writable” State:

1. On the array:

a) Free up space on the volume or increase the volume quota.

b) Volume goes into online state if it is no more violating the space policy.

2. On ESX, hit “Resume” on the “stunned” VM

Note :  If the volume quota is set to 100% you will never overrun the volume and it will not enter in the Non-writable state. The quota needs to be set to 99% or lower to see this behavior.

B. Now what happens on Windows 2012 ?

On windows 2012 Thin Provisioning Space Threshold Warning is eventID 144


1. On the array:

a) Free up space on the volume or increase the volume quota.

b) Volume goes into online state if it is no more violating the space policy.

2. On Windows The marked offline disk needs to be set online again by the administrator

Okay guys & girls. That was it for now. Enjoy the new functionalities.

About the Author


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