VSAN Configuration

In the last blog post I covered the VSAN Prerequisites, now it’s time to configure VSAN.  For the sake of completeness I had already configured a vDS with a port group named VSAN_VLAN20 as shown in the screenshot below.


Enabling VSAN

Enabling VSAN is a one click operation at the Cluster level.  Simply tick to Turn On Virtual SAN


  • Automatic enables VSAN to claim SSD and SATA and form a disk group on each ESXi Host
  • Manual enables the vSphere administrator to manually assign disks to the disk group on each ESXi Host

For my deployment ‘Automatic’ was the logical choice as I had already created a VMFS volumes on my local datastores on each ESXi Host and therefore VSAN would be unable to claim them.

Under Disk Management I can see the disk group which has been created and the local disks which have been assigned into the disk group.


Storage Policy

VSAN automatically creates storage policies which are exposed via VASA when VSAN is enabled.  The storage policies available are:

  • Number of Failures to Tolerate
    • VSAN creates a RAID 1 copy of the working data set, with a witness on a third ESXi Host.  If the policy is set to 1 then 2 copies of each data set are created.  If the policy is set to 2 then 3 copies of each data set are created.
  • Number of Disk Stripes Per Object
    • An object is striped across magnetic disks to potentially increase performance.  Two things to bear in mind here, the first that if you have multiple magnetic disks in a disk group, then VSAN might stripe across those and the second is that a stripe width greater than one should only be used if you are getting read cache misses that cannot be served from a single magnetic disk e.g. VM requires 400 I/O
  • Flash Read Cache Reservation
    • Provides the ability to specify in percentage terms how much of an SSD is used for read cache e.g. 100GB VM with 1% policy would use 1GB on a 250GB SSD
  • Object Space Reservation
    • Provides the ability to reserve all space upfront using Lazy Zeroed Thick

Note: If you do not define a Storage Policy VSAN automatically defaults to ‘Number of Failures to Tolerate equals 1’

I have created a Storage Policy called VSAN Failure To Tolerate 1.  When you click on ‘Rules Based on Vendor Specific Capabilites’ and select ‘VSAN’ the above Storage Policies are presented and you can select which policy is required.


Virtual Machines

The last thing to do is migrate virtual machines across to the VSAN Datastore.  This is a straight forward operation which only requires the vSphere administrator to select the correct Storage Policy.


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