Large resync operation after vSAN storage policy change

Products

• VMware vSAN

Issue/Introduction

• vSAN Cluster might trigger a large resync after changing the Storage policy for the Virtual machines.
• vCenter UI > Cluster > Monitor > vSAN > Resyncing Object will show the amount of data to resync and estimated time to complete the resync.
  
  
  
  
• From Host CLI, we can verify the resync details using the below command.
  
# localcli vsan debug resync summary get

ResyncSummary:
   Total Number Of Resyncing Objects: 2
   Total Bytes Left To Resync: 1385384650997
   Total GB Left To Resync: 1290.24

Environment

VMware vSAN (All version)

Cause

Rsync is an expected behaviour after the storage policy change for a Virtual machine in a vSAN cluster. Resync is performed by the cluster automatically to make the vSAN objects of the Virtual machines compliant with newly applied storage policy.

Following are the scenarios of resync in a Storage policies change.

Change in Storage policy	Resync
RAID-1 to RAID-1 with higher FTT	Yes
RAID-1 to RAID-1 with lower FTT	No
RAID-1 to RAID-5/6	Yes
RAID-5/6 to RAID-1	Yes
RAID-5 to RAID-6	Yes
RAID-6 to RAID-5	Yes
Changing the Disk stripes per object	Yes
Changing the Object space reservation	No
Disabling Checksum	No
Enabling Checksum	Yes

 

Resolution

This is an expected behaviour in the vSAN Cluster.

In case of any issues with resync stuck or any other issues during resync, please contact the Broadcom Support.