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TPS (Transparent Page Sharing) and UNMAP

TPS (Transparent Page Sharing) and UNMAP are distinct VMware vSphere features that address different aspects of resource management. TPS focuses on memory optimization by deduplicating identical memory pages across virtual machines, while UNMAP, a SCSI command, enables thin-provisioned storage arrays to reclaim unused space by identifying and discarding deleted blocks. 

TPS (Transparent Page Sharing): 

Function:

TPS identifies and consolidates identical memory pages used by multiple VMs, reducing overall memory consumption. 

Mechanism:

It works by comparing the content of memory pages and storing only one copy if they are identical, effectively deduplicating memory. 

Intra-VM vs. Inter-VM:

TPS can operate within a single VM (intra-VM) or across multiple VMs (inter-VM). 

Security Considerations:

While TPS can enhance memory efficiency, it also presents a potential security risk as it can be exploited to access data on other VMs. VMware has addressed this by introducing changes to TPS behavior, including restricting inter-VM TPS by default. 

UNMAP: 

Function: UNMAP is used to reclaim unused space on thin-provisioned storage arrays. It informs the storage array that certain blocks are no longer in use and can be returned to the free pool. 

Mechanism: UNMAP is a SCSI command sent by the hypervisor to the storage array, indicating which blocks are no longer needed. 

Benefits: UNMAP allows for better utilization of storage capacity by allowing the array to reuse freed blocks. 

VMFS-6: UNMAP is automatically enabled for VMFS-6 datastores. 

Monitoring: You can monitor UNMAP operations using tools like esxtop. 






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