vSAN OSA cache tier capacity upgrade to 1.6TB

Introduction

Since vSphere 8.0 it’s now possible to increase the cache tier capacity from 600 GB to 1.6TB for full flash vSAN infrastructure.
This capacity allows to vSAN OSA design to deal more IO on the Cache tier in write mode before acquitting them on the Capacity tier.

Before vSphere 8 the vSAN cache tier was limited to 600GB, since vSphere 8 with the new vSAN format, VMware increased this limit to 1.6TB

Prerequisite

• Having a Full Flash vSAN OSA
• vCenter, ESXi, and vSAN in version 8 or higher
• On-disk format in version 17 or higher

Procedure

BringUP vSAN/VxRail/VCF

Before starting the BringUP
Connect on each host by SSH or ESX CLI and run this command

esxcfg-advcfg -s 1 /LSOM/enableLargeWb

Verify that the parameter is correctly applied

esxcfg-advcfg -g /LSOM/enableLargeWb

Installed vSAN cluster

After your vSAN is deployed you have also the possibility to do the configuration, but to apply it you need to recreate all disk groups.

Usually, I use PowerCLI for doing this type of configuration, because it’s not needed to connect on each ESXi….. also if you have time you can re-use the command “esxcfg” on each ESXI or you can use this oneliner:

Configuration:

get-cluster NameOfTheCLuster | get-vmhost | get-AdvancedSetting -Name "LSOM.enableLargeWb" | Set-AdvancedSetting -Value "1"

Verification:

get-cluster NameOfTheCLuster | get-vmhost | get-AdvancedSetting -Name "LSOM.enableLargeWb"

Now the last step will be in the vSphere interface:

• Select the cluster in the vSphere inventory
• Go to Configure tab
  • vSAN => Disk Management
• For each ESXi click on VIEW DISKS
  • For Each disk group click on the three dots and select Recreate
  • Select the vSAN Data Migration to Ensure Accessibility or Full Data Migration (This choice depends on your internal policy)
  • Go to Precheck
    • If precheck is green => Recreate
    • This process will take time in function of the data that is needed to be copy

If you want to monitor that the buffer is now at 1.6TB, you can do this:

• Select one ESXI in the inventory
• Go to Monitor tab
  • vSAN => Performance
  • DISKS
    • Select a Disk Group
    • Check Capacity and Usage

That’s it,

Thanks for your reading,

Cheers,

Valentin