vSAN Health Service - Limits Health – Current Cluster Situation

Products

VMware vSAN

Issue/Introduction

This article explains the Limits Health – Current Cluster Situation check in the vSAN Health Service and provides details on why it might report an error.

Symptoms:
ESXi Versions 6.x

Resolution

Q: What does the Limits Health – Current Cluster Situation check do?

This particular health check looks at free disk capacity and ensures that the components per host limit has not been exceeded, and that there is some flash read cache capacity remaining (Note: Flash read cache is only relevant to hybrid configurations and is not relevant on all-flash configurations).

Note: VMware recommends that the disk capacity maintains a slack space of 30% to avoid excessive re-balance operations. Also note that this way of looking at the resources has some limitations. For example, if there are 3 ESXi hosts in a vSAN cluster, and 2 ESXi hosts are filled to capacity while one is empty, the cluster summaries may look like there are plenty of free resources across all 3 ESXi hosts. However, virtual machine provisioning may fail, as vSAN will require capacity on at least 2 ESXi hosts for the 2 replicas that it needs to create.

Q: What does it mean when it is in an error state?

If this check has a warning or error, it may means that the number of components has reached its ESXi host limit, or that there is no free storage capacity, or that the flash read cache reservations have been exhausted. If components limits have been reached, or there is no free capacity, the deployment of new virtual machines fails, nor a rebuild operations can be allowed. If the flash read cache is exhausted, it means that there is very little read cache available for those virtual machines that do not have reservations. This will impact the performance of these virtual machines.

The following thresholds apply to this Current Cluster Situation health check.

Component utilization :-

•   Red: utilization > 90% for any host in this cluster;
•   Yellow: utilization <= 90% while utilization > 80% for any host in this cluster;
•   Green: utilization <= 80% for any host in this cluster;

Disk space utilization :-

•   Red: utilization > 90% for any disks of any host in this cluster;
•   Yellow: utilization <= 90% while utilization > 80% for any disks of any hosts in this cluster;
•   Green: utilization <= 80% for any all the disks in this cluster;

Read cache reservations :-

•   Red: utilization > 90% for any host in this cluster;
•   Yellow: utilization <= 90% while utilization > 70% for any host in this cluster;
•   Green: utilization <= 70% for any host in this cluster;

This table displays the thresholds at which warnings and errors are displayed in this health check:

Resourcevsan.check_limits and vsan.disks_stats. For more information, see the Troubleshooting vSAN Storage section in the VMware vSAN Diagnostics and Troubleshooting Reference Manual .

For component limits per host and cluster, refer below article :-

vSAN Health Service - Limits - Host component : https://kb.vmware.com/s/article/2146130
vSAN Component Limit per Cluster : https://kb.vmware.com/s/article/74695

Additional Information

For more information on collecting VMware vSAN logs, see Collecting vSAN support logs and uploading to VMware (2072796).

Also, see: