Last week VMware released an urgent hotfix to remediate potential data loss in vSAN 6.6.1 due to resynchronisation mixed with object expansion.
This is a known issue affecting earlier versions of ESXi 6.5 Express Patch 9. The vendor states that a sequence of the following operations might cause it:
- vSAN initiates resynchronisation to maintain data availability.
- You expand a virtual machine disk (VMDK).
- vSAN initiates another resync after the VMDK expansion.
Detailed information about this problem is available in KB 60299.
If you are a vSAN customer, additional considerations are required before applying this hotfix:
- If hosts have already been upgraded to ESXi650-201810001, you can proceed with this upgrade,
- If hosts have not been upgraded to ESXi650-201810001, and if an expansion of a VMDK is likely, the in-place expansion should be disabled on all of them by setting the VSAN.ClomEnableInplaceExpansion advanced configuration option to ‘0‘.
The VSAN.ClomEnableInplaceExpansion advanced configuration option is not available in vSphere Client. I use the following one-liner scrips to determine and change its value via PowerCLI:
# To check the current status
Get-VMHost | Get-AdvancedSetting -Name “VSAN.ClomEnableInplaceExpansion” | select Entity, Name, Value | Format-Table -AutoSize
# To disable the in-place expansion
Get-VMHost | Get-AdvancedSetting -Name “VSAN.ClomEnableInplaceExpansion” | ? {$_.Value -eq “1”} | Set-AdvancedSetting -Value “0”
Note: No reboot is required after the change.
After hosts were upgraded to ESXi650-201810001 or ESXi650-201811002, you can set VSAN.ClomEnableInplaceExpansion back to ‘1‘ to enable the in-place expansion.
LIFE IN A VIRTUAL SPACE 