"Compression only" enabled disks reach 100% full

Products

• VMware vSAN

Issue/Introduction

This article provides information on "Compression only" which may fill up disks faster than expected (compared to with deduplication and compression).

Symptoms:
On a vSAN environment where "Compression only" is enabled and physical disks are smaller than 1 TB, you see this symptom:

The vSAN health check for physical disk capacity is red/yellow for some disks.

Environment

VMware vSAN 7.0.x

Cause

This issue occurs when using "Compression only" with capacity disks that are less than 1 TB, capacity usage can change more quickly than vSAN can react with rebalancing, which may lead to disks becoming full.

Resolution

This is a known issue affecting VMware vSAN 7.0 Update 1.

Currently, there is no resolution.

Workaround:
To work around this issue, lower both the reactive rebalance and automatic rebalance thresholds.

1. Set the reactive rebalance threshold advanced configuration option /VSAN/ClomRebalanceThreshold to 60% on all ESXi hosts using the following steps:

1.  In the vSphere client, select the host in the vSAN cluster
2. Click Configure
3.  Select System >  Advanced System Settings
4.  Edit and filter for ClomRebalanceThreshold
5.  Select ClomRebalanceThreshold and adjust Value to 60%

2. Set the automatic rebalance variance threshold to 20%. For more information, see the Configure Automatic Rebalance section of the vSAN Monitoring and Troubleshooting Guide.