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


Article ID: 326590


Updated On:


VMware vSAN


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


VMware vSAN 6.x


  • 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. 


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":

Object Space Reservation is changed in the assigned Policy by clicking "Edit":
HTML Client:

Flash Client:
(Via clicking "Add rule" Object Space Reservation is being added)