vSAN -- Enabled: Deduplication & Compression -- Low Ratio / Object Space Reservation at 100%

Products

• VMware vSAN

Issue/Introduction

Symptoms:
Deduplication/Compression ratio can be low when thick objects are being used.

Environment

VMware vSAN 6.x

VMware vSAN 8.x

Cause

• The objects in vSAN are applied policy with 100% Object Space Reservation (OSR).
• The UI the storage values indicate the deduplication/compression did not occur and we mark the space as used.
• This is by design. When OSR is 100%, all of the space is reserved for that VM alone and dedupe/compression will not help as other VMs are not allowed to use this space.
• In many cases the OSR =100 VMDK are overwritten with zero by vmkfstools -w "paht to vmdk" to ensure all the space is consumed and cleared. 

Resolution

These issues has been resolved in 7.0 where the space utilization in OSR=100 is considered as thick. 

However , if you want  space saving on a disk you may need to change the storage policy back to OSR=0 which will free up the unused free space reserved by OSR=100 

The deduplication/compression ratio will increase because we drop the reservation, and report on the actual physical (possibly deduped) usage.

See here for definition of "Object Space Reservation":
https://techdocs.broadcom.com/us/en/vmware-cis/vsan/vsan/8-0/vsan-administration/using-vsan-policies/about-vsan-policies.html

Object Space Reservation is changed in the assigned Policy by following the below KB: 
https://techdocs.broadcom.com/it/it/vmware-cis/vsan/vsan/8-0/vsan-adminstration-7-0/using-vsan-policies.html

 

Additional Information

vSAN - Deduplication is not showing any space savings