Backup or Snapshot failures on vSAN cluster with 'Out of resources' error

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

When attempting to perform a virtual machine (VM) backup or create a manual snapshot in a 5 node vSAN cluster, the task fails with one or more of the following errors in vCenter Server:

• An error occurred while taking a snapshot: Out of resources.
• No disks of required version is present in the cluster for this operation to succeed.

Additionally, the vmware.log for the affected VM may contain entries similar to:

vcpu-0 - OBJLIB-VSANOBJ: VsanObjCreateInt: Failed to create object: No space left on device (1835010).
vcpu-0 - DISKLIB-LINK : DiskLinkCreate: Failed to create extent: Out of resources
vcpu-0 - SNAPSHOT: SnapshotBranch failed: Out of resources (5).

During the time of the issue one host was in maintenance mode.

Environment

VMware vSAN (all versions)

Cause

• This issue occurs when the vSAN cluster does not have enough active hosts to satisfy the requirements of the assigned vSAN Storage Policy during a snapshot operation.
• In this specific scenario, the VM was governed by a RAID 1 (Mirroring) - Failures to Tolerate (FTT) 2 policy. This policy requires a minimum of 5 active hosts (2n+1 where n=2, plus witnesses/replicas) to maintain quorum and data redundancy.
• If one or more hosts are placed into Maintenance Mode (even with the 'Ensure Accessibility' option), the number of available hosts falls below the minimum required by the policy (e.g., 4 hosts available instead of 5), preventing the creation of new snapshot objects.

Resolution

To resolve this issue, ensure the vSAN cluster meets the minimum host requirements for the configured storage policy:

1. Identify the storage policy assigned to the affected virtual machine(s) by navigating to VM > Configure > Policies.
2. Confirm the number of active hosts required for that policy (e.g., FTT=1 requires 3 hosts, FTT=2 requires 5 hosts for RAID 1).
3. Check the status of all ESXi hosts in the cluster. If any hosts are in Maintenance Mode, they must be exited to restore full cluster resources.
4. Once the required number of hosts are active and connected, retry the backup or snapshot operation.

Refer below kb to see the minimum number of hosts required for each Raid policy with the FTT selected:

Clarification on vSAN "Fault domain failures to tolerate” as displayed under Cluster - Configure - Fault Domains

Additional Information

If a host must remain in maintenance mode for an extended period, you may temporarily change the VM's storage policy to a lower redundancy level (e.g., from FTT=2 to FTT=1) to allow snapshots to proceed.

Note: This will reduce the data redundancy for that VM until the original policy is reapplied.