vSAN Snapshot Failures on Large Virtual Machines in vSAN cluster

Products

• VMware vSAN

Issue/Introduction

• Virtual machines with massive data footprints (e.g., 38+ TB) may experience snapshot failures with the error "Out of resources (5)" when governed by RAID 5 storage policies. This occurs because the snapshot process requires significant datastore headroom to accommodate delta files and parity/redundancy overhead.

Symptoms :

• Snapshot task fails in vCenter.
• Error message: "An error occurred while taking a snapshot: Out of resources."
• Log entry (vmware.log): SnapshotVMXTakeSnapshotComplete: Snapshot 0 failed: Out of resources (5).

Environment

VMware vSAN 8.x

 

Cause

• RAID 5 policies provide space-efficient redundancy but impose specific requirements on datastore free capacity. For very large VMs, the creation of a snapshot necessitates an immediate allocation of free space to store delta files, which can exceed the currently available headroom.

vmware.log :

Z vcpu-0 #######-1059658-auto-####-h5:########-c#-##-#### SnapshotVMXTakeSnapshotComplete: Snapshot 0 failed: Out of resources (5)

Resolution

1. Analyze Capacity: Calculate the required snapshot headroom. For RAID 5 configurations on VMs exceeding 30 TB, ensure sufficient available datastore capacity exists to accommodate at least 30-50% overhead for snapshot delta files, depending on change rates.
2. Expand Datastore: If the datastore is at capacity, add additional storage nodes or disk groups to the vSAN cluster to provide the necessary headroom.
3. Optimize Storage: Temporarily clear stale snapshots, orphaned files, and unneeded data across the datastore to free up operational space.
4. Policy Review: Assess if a RAID 5 policy is strictly necessary for the affected VM or if temporary policy modification is feasible during maintenance windows, though this is not recommended for long-term production.

Additional Information

• Log Retrieval: To learn how to retrieve and analyze logs for snapshot failures, refer to Retrieving vSphere Logs.
• Support: To speak with a customer representative or a Support Engineer, see Contact Support.
• Note: For defects and enhancements, ensure you subscribe to this article (reference: https://knowledge.broadcom.com/external/article/275360) to be updated on fix status.