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AVS and CBS Troubleshooting: VMFS and CBS Capacity Issues

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As an external block storage provider, Pure Cloud Block Store (CBS) can provide VMFS datastore to Azure VMware Solution (AVS) clusters. Like any sort of datastores, they get populated and filled with Virtual Machine provisioned disks. It is the customer's responsible to monitor and keep an eye on the datastore capacity utilization, and the CBS array usable capacity. 

This KB will cover a couple of common problems associated with capacity utilization and what is the impact on the platform once you hit the physical capacity limits.  Furthermore, it will go through solutions for each issue and how to prevent from getting into the capacity issues. 

Problem 1: vCenter Alert "A VMFS datastore is full" 

If left unchecked, the VMFS datastore reach maximum capacity with Virtual Machine files or other files, when it gets full, vCenter will send alerts. 

Problem 2: CBS Alert "Array Storage Consumption has Reached X% of Usable Capacity" Alert #25 

The array will also send warning alerts by default when the used capacity gets to 80%, 90%,95% threshold. For more information check Alert #25 


Capacity issues can have a significant impact on the performance and reliability of CBS on AVS. If left unresolved, these issues can lead to data loss and downtime.

Impact from Problem 1: VMFS is a core element of the ESXi host. As VMFS nears full capacity, it can impact the Virtual Machine startup as there will be no space for .vswp file to be created. It can also lead to performance degradation for the powered on VMs, not to mention other unpredictable behavior. Refer to this VMware KB.   

Impact from Problem 2: Alert #25 has three thresholds at which it will alert: 80%, 90%, 100%.  These alerts serve as a warning for the Pure Cloud Block Store Administrator about an upwards trend in space consumption.  If the array fills up on space usage, without correction, you may suffer an outage.


Here are the troubleshooting steps for resolving capacity issues in Pure Cloud Block Store on Azure VMware Solution:

Solutions 1: Extend the capacity of VMFS datastore attached to the AVS cluster

All VMFS datstores must retain a level of free space to ensure that the virtual machines will function properly. To increases the size of an existing CBS VMFS datastore, customers can access the Pure VMware Cloud Manager PowerShell environment, then execute the following command after passing the datastore name and the desired new capacity.

Set-PCBSVmfsCapacity -ClusterName "mycluster" -DatastoreName "myDatastore" -Size 800GB -AVSCloudName "myAVSCloudName" -AVSResourceGroup "myAVSResourceGroup"

More information about how to manage the AVS and CBS storage integration can be found here.

Solutions 2: Upgrade the overall usable capacity of CBS array. 

For arrays running Purity version lower than 6.6.2, the capacity upgrades process of the array is a support driven task. Support cases can be opened by email and requesting a CBS capacity expansion. Pure Support engineers may have previously reached out to you once the array capacity hit 88% consumption. 

For CBS arrays running Purity version 6.6.2 and above, customer can perform array capacity upgrade on-demand using the Pure CLI. Follow this KB for the HOW-TO steps Customer-Driven Capacity Upgrades