How to convert a vSAN ESA (Express Storage Architecture) cluster to an OSA (Original Storage Architecture) cluster

Products

• VMware vSAN

Issue/Introduction

To convert a vSAN ESA (Express Storage Architecture) cluster to an OSA (Original Storage Architecture) cluster, we need to completely rebuild the cluster by removing all existing vSAN storage configurations on the hosts and then reconfigure them using the OSA settings within the vSphere web client.

 

This process involves migrating away from the single storage pool used in ESA to the traditional disk group structure of OSA, which requires defining separate cache and capacity devices on each host

 

Key points to remember:

• Data Migration:

  • This process would likely involve migrating VMs to another cluster or temporarily expanding storage capacity to ensure no data loss during the conversion.
  • Alternatively Adding VMFS or NFS datastore to temporarily migrating the data out from vSAN. 

• No Direct Conversion Tool:

  • VMware does not offer a direct conversion tool to switch between ESA and OSA, requiring a complete reconfiguration. 

• Hardware Compatibility:

  • Ensure your hardware is compatible with OSA requirements, which may include having separate flash devices for caching if not already present. 

 

Environment

vSAN ESA 8.x 
vSAN OSA 8.x 

Cause

• ESA uses only SSDs and NVMe drives and does not separate cache and capacity disks in the vSAN disk group, as it follows a single-tier architecture. 

• On the other hand, OSA requires defining separate cache and capacity devices on each host, as it follows a multi-tier architecture.

• Therefore, converting ESA to OSA is a destructive process due to the architectural differences between the two vSAN configurations

Resolution

Note: Before following the steps from the KB, please take a restorable backup of the vSAN environment, as the steps will completely erase the data.

 

Here are the steps to remove ESA configuration from your setup and configure an OSA vSAN cluster: 

• Backup Data:
  
  
• • Back up all virtual machines on the ESA cluster to a safe location. 
  • If intending to use virtual machines while vSAN is off, make sure to migrate virtual machines from the vSAN datastore to another datastore before turning off the vSAN cluster

• Remove Existing vSAN Configuration:

• • Access the vSphere web client and navigate to the ESA cluster.
  • Reference KB to disable vSAN cluster : Enabling or disabling a vSAN cluster
  • Once the vSAN is turned off please follow below steps to ensure there are no vSAN ESA disk configuration on vSAN ESA Nodes. 

Option 1 -  Via vSphere UI:  

• • Need to remove partition information from a device so vSAN OSA can claim the device for use.
    • Verify that the device is not in use by ESXi as boot disk, VMFS datastore, or vSAN.
    • If you have added a device that contains residual data or partition information, you must remove all preexisting partition information from the device before you can claim it for vSAN use. VMware recommends adding clean devices to disk groups.
    • When you remove partition information from a device, vSAN deletes the primary partition that includes disk format information and logical partitions from the device.
    • Navigate to the vSAN cluster.
    • Click the Configure tab.
    • Under vSAN, click Disk Management.
    • Select a host to view the list of available devices.
    • From the Show drop-down menu, select Ineligible.
    • Select a device from the list and click Erase partitions.
    • Click OK to confirm.
    • The device is clean and does not include any partition information.  

 

Option 2 -  Via ESXCLI :  

• • clean the disk partition info from command line with the help of following KB:  
    • How to manually manage and configure a vSAN disk group using esxcli commands 

[root@esxi1:~] localcli vsan storagepool  list

mpx.vmhba0:C0:T1:L0:
   Device: mpx.vmhba0:C0:T1:L0
   Display Name: mpx.vmhba0:C0:T1:L0
   vSAN UUID: 5225#################0579f7
   Used by this host: false
   In CMMDS: false
   On-disk format version: 19
   Checksum: 10090812040429352287
   Checksum Ok: true
   Is Mounted: true
   Is Encrypted: false
   Disk Type: singleTier
   Creation Time: Wed Sep  6 14:57:34 2023

[root@esxi1:~] localcli vsan storagepool remove -u 5225#################0579f7
[root@esxi1:~]

• Reconfigure with OSA settings:

• • On the "Configure" tab, select "vSAN" again and choose "Configure" to launch the wizard. 
  • Select "vSAN OSA" as the storage architecture.
  • Define disk groups on each host, specifying separate cache and capacity devices as needed.
  • Configure fault domains and other relevant settings. 
    
    

• Migrate VMs back:

  
  
  • Once the OSA cluster is set up, migrate VMs back from the backup location to the newly configured OSA cluster. 

 

Additional Information

Important Considerations:

• Performance Impact:

  • Converting from ESA to OSA might affect performance depending on your workload profile, as ESA is designed for high performance with a single storage pool.
    
    

• Compatibility Check:

  • Ensure your hardware is compatible with OSA requirements before proceeding.