Unable to Download .vmem and .vmsn Files with Actual Size for VMs on vVOL/vSAN Datastore for Crash Dump Creation

Products

• VMware vSphere ESXi

Issue/Introduction

Symptoms:

• The download size for vmem and vmsn files is displayed in kilobytes instead of the actual file size

• When VMs are residing on vVol/vSAN Datastore 
• The same files download with correct size when its on VMFS datastore 
• Failure to create a memory dump file for Guest OS PSOD analysis, and the following error was received:

mmss2core version 8456865 Copyright (C) 1998-2017 VMware, Inc. All rights reserved.
region[@]: start=0 end=c0000000.
region[1]: start=100800000 end=448800000.
Cannot read long mode root CR3=1amdee rootOffs=1aa0ee.
Cannot translate linear address fffff78000000000.
Cannot read 0x10900000 bytes at 0 past end of memory.

Environment

VMware vSphere ESXi 7.x
VMware vSphere ESXi 8.x

Cause

vVol and vSAN datastores utilize an object-based storage architecture. In these environments, memory states and snapshot data are stored as distributed objects managed by the storage hardware. The files visible in the datastore browser are descriptor (pointer) files. Because the data is distributed across multiple objects, the individual pointer file size is displayed in kilobytes.

Resolution

To download the full data payload for memory dump creation, the underlying objects must be bundled during the download process. Follow these steps:

1. Log in to the vSphere Client.
2. Navigate to the Datastores tab for the affected Virtual Machine.
3. Browse to the Virtual Machine folder on the datastore.
4. Locate the .vmem and .vmsn files.
5. Select both the .vmem and .vmsn files simultaneously (use Ctrl+Click).
6. Click Download.
   Note: This triggers vCenter to package the distributed objects into a single .zip archive containing the full data.
7. Extract the downloaded .zip archive.
8. Verify that the extracted .vmem file size matches the RAM provisioned to the Virtual Machine.
9. Run the vmss2core tool to generate the memory dump.

Additional Information

• For general instructions on using the conversion tool, see Converting a snapshot file to memory dump using the vmss2core tool
• For issues involving encrypted VMs see Converting virtual machine snapshots to memory dumps in VMware vSphere