Write-cache disabled on storage array causing performance issues or failures

Products

• VMware vCenter Server
• VMware vSphere ESXi

Issue/Introduction

• Poor disk I/O performance to the storage array, causing very slow or the failure of:
  
  • Template deployments
  • Cold migrations
  • vMotion
  • VMware Consolidated Backup
    
    
• In cases where the ESX/ESXi environment is large, write caching suddenly becoming disabled can result in a performance degradation that makes communication to the LUNs impossible. If this occurs, you may experience these symptoms:
  
  • Virtual machines fail or stop responding.
  • High device latency (DAVG) values seen via esxtop
  • VMFS datastores go off-line with the following error message in the logs:
    
    Lost heartbeat

Environment

VMware Consolidated Backup 1.1.x
VMware ESX Server 3.0.x
VMware ESXi 4.1.x Installable
VMware vCenter Server 4.1.x
VMware ESXi 4.0.x Embedded
VMware ESXi 3.5.x Installable
VMware vCenter Server 4.0.x
VMware ESX Server 3.5.x
VMware VirtualCenter 2.0.x
VMware VirtualCenter 2.5.x
VMware vSphere ESXi 5.0
VMware Consolidated Backup 1.0.x
VMware Consolidated Backup 1.5.x
VMware ESXi 3.5.x Embedded
VMware vSphere ESXi 5.5
VMware ESX 4.1.x
VMware ESXi 4.1.x Embedded
VMware ESXi 4.0.x Installable
VMware vSphere ESXi 5.1
VMware ESX 4.0.x

Resolution

Write caching must always be enabled.

On many arrays, write caching is automatically turned off when:

• The battery backup is disconnected
• The battery backup fails
• One of the redundant power supplies disconnects or fails.

To ensure that write caching does not become disabled, VMware recommends that you have a battery backup connected.

Note: For more information on enabling write-cache, contact your storage hardware vendor.