vSAN Health Service - Capacity utilization - Read cache reservations

Products

• VMware vSAN

Issue/Introduction

This article explains the Capacity utilization health – read cache reservation in the vSAN Health Service and provides details on why it might report an error.

Environment

VMware vSAN 6.7.x

Resolution

Q: What does the Capacity utilization health – Read cache reservations check do?

This particular health check looks at free read cache and posts an alarm when exceeding existing preset thresholds.
Note: Flash read cache is only relevant to hybrid configurations and is not relevant on all-flash configurations. This health check has been deprecated and won’t be shown in the vSAN skyline health UI for vSAN clusters running version 7.0 U1 or later.
 

Q: How does one troubleshoot and fix the error state?

If this check has a warning or error, it indicates the flash read cache reservations have been exhausted and there is 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 health check.

• 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;