Storage space utilization calculation for VM's objects on vSAN Express Storage Architecture (ESA) datastore

Products

• VMware vSAN

Issue/Introduction

This article explains the used space calculation for VM's objects that reside on vSAN Express Storage Architecture (ESA) datastore.

Environment

VMware vSAN 8.x - Express Storage Architecture (ESA)

Resolution

• In vSAN ESA, following overheads are added for each object upon object provision.

• If an object is thick provisioned, these overheads are allocated immediately and capacity is consumed. If the object is thin provisioned, overheads will be based on the amount of IO written on the object.

• The overheads are:

  1. Object replica data

     • This is the storage overhead which gets consumed as per the RAID policy used.

     • For RAID1 it will be equal to 100% of the primary copy of data.

     • For RAID5 it will be equal to 25% of the primary copy of data.

     • For RAID5(2+1) it will be equal to 50% of the primary copy of data.

     • For RAID6 it will be equal to 50% of the primary copy of data.

  2. vSAN LFS overheads for the object

     • This overhead helps the vSAN Log-structured file system (LFS) for the given object process and stores aspects of the LFS that helps deliver the high performance associated with the Express Storage Architecture.

     • This will consume an additional ~13.1% of the object and replicate data size.

Below are some examples showing how the object space utilization is calculated in vSAN ESA: 

Sl. No.	Storage Policy	Provisioned Object Size	Actual Data Written	Object Size with RAID Factor (Data written + Object replica data)	Object's vSAN LFS Overhead - 13.1%	Total Object Space Utilization
1.	RAID1-Thin	20 GB	10 GB	20 GB	2.62 GB	22.62 GB
2.	RAID5-Thin	20 GB	10 GB	12.5 GB	1.63 GB	14.13 GB
3.	RAID6-Thin	20 GB	10 GB	15 GB	1.96 GB	16.96 GB
4.	RAID5(2+1) Thin	20 GB	10 GB	15 GB	1.96 GB	16.96 GB
5.	RAID1-Thick	20 GB	10 GB	40 GB	5.24 GB	45.24 GB
6.	RAID5-Thick	20 GB	10 GB	25 GB	3.275 GB	28.27 GB
7.	RAID6-Thick	20 GB	10 GB	30 GB	3.93 GB	33.93 GB
8.	RAID5(2+1) Thick	20 GB	10 GB	30 GB	3.93 GB	33.93 GB

Additional Information

For more information refer Capacity Overheads for the ESA in vSAN 8