VM backup getting slow, suspecting while taking snapshot for backup from Commvault it getting slow.

Products

• VMware vSAN

Issue/Introduction

• Virtual machine backups using Commvault perform slowly or fail during the snapshot phase.
• Manual snapshot creation on the affected virtual machine may fail or experience significant delays.
• In the Commvault or VDDK logs, you observe the following error sequence:

error -[268680] [Originator@6876 sub=DiskLib] DISKLIB-CHAIN : DiskChainDBGet: Cannot apply logicalSectorSize to partial chain. error -[268680] [Originator@6876 sub=DiskLib] DISKLIB-CHAIN : DiskChainDBGet: Cannot apply physicalSectorSize to partial chain. VixDiskLib: Detected DiskLib error 1441801 (Invalid argument). VixDiskLib_Read: Read 1 sectors at 0 failed. Error 3 (One of the parameters was invalid)

Environment

• VMware vSphere ESXi 7.x / 8.x
• VMware vSAN (OSA and ESA)
• Commvault Backup Solution using HotAdd transport mode

Cause

This issue occurs when existing manual snapshots create a conflict or a 'partial chain' within the Virtual Disk Development Kit (VDDK). When the backup tool attempts to open the disk chain, it cannot reconcile the sector size metadata across the existing delta files and the new snapshot being requested. This is often exacerbated when snapshots are left on the VM for extended periods or when automated cleanup tasks fail.

Resolution

To resolve the disk chain conflict and restore backup performance, perform the following steps:

1. Identify and Remove Manual Snapshots:

   • In the vSphere Client, navigate to the affected Virtual Machine.
   • Select Snapshots > Manage Snapshots.
   • Identify any manual or stale snapshots and select Delete All to merge the delta disks into the base disk.

2. Perform Disk Consolidation:

   • If the snapshot manager shows no snapshots but the issue persists, right-click the VM and select Configure > Snapshots > Consolidate.
   • Monitor the task to ensure successful completion.

3. Reset Changed Block Tracking (CBT) (Optional):

   • If slowness persists after consolidation, refer to Virtual machine experiences very long stun time during snapshot creation with CBT enabled for steps to reset CBT while the VM is powered off.

Additional Information

• Best practices for using VMware snapshots in the vSphere environment
• Changed Block Tracking (CBT) on virtual machines