Unable to Download .vmem and .vmsn Files with Actual Size for VMs on vVOL 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 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 datastores use a different architecture compared to traditional VMFS datastores. They are exported as objects by a storage system and are managed entirely by hardware on the storage side. 
• When a snapshot is taken in a vVol environment, the snapshot delta files (which record changes since the snapshot) are stored in a vVol-backed LUN or storage container. This means the snapshot data is not stored in a single, large file like in traditional VMFS datastores but is rather distributed across multiple vVol objects based on the storage policy applied. 
• Since its is distributed across multiple vVol objets the size of the file is shown in kilobytes. 

 

Resolution

Follow below Steps to download .vmsn and .vmem files  

 

• Find the Datastore of the VM by clicking datastores of the VM 

Select VM --> Click on Datastores 

• Search for the files using below path 

Click on Datastore --> Files -->Browse Virtual machine folder --> Check for vmem and vmsn files --> Select both files at same time and click -->download 

• Go to Downloads and check the file size it should be actual memory and snapshot size of the VM

After this, the zip file can be used to create a memory dump for PSOD VM analysis

   Note :Downloading a single file results in it being downloaded in kilobytes, making it unusable for memory dump creation

 

Additional Information

Steps to create memory dump files for windows VM in VMware environment 

• Log into the ESXi host or vCenter where the VM is hosted.
• Right-click on the VM and select Power > Power Off or Reset if the VM is not responding.
• If the VM has crashed, you can find the VM's memory dump files in the datastore. These will be typically stored in the VM’s folder on the datastore with filenames like vmname.vmem 

To create a memory dump file we need vmsn and vmem file together 

•  Download both the files(vmsn and vmem)  from respective datastore and extract those files 
•  Download the utility file by following below KB article 

                    Converting a snapshot file to memory dump using the vmss2core tool

•   Open command prompt and run below command to create memory dump (Copy the location of dump files and go that location and run below command)             

                  vmss2core-new-sb-8456865.exe -W8 xxxxxxx.vmsn xxxxx.vmem

             

             

       4.  Memory file created successfully.

          

Note : For vSAN datastore  use below documentation 

          Generate .vmem and .vmss files for VMs running on the vSAN cluster