Support for TRIM and UNMAP commands allows vSAN clusters to reclaim space when files are deleted in a VM or when space is allocated for multiple writes to the same file.
Provisioning virtual machines with thin-provisioned disks allows you to conserve storage space. The disk starts small, and expands to accommodate the storage space needed by the guest operating system, up to the maximum disk size allocated.
Even with thin provisioning, there are obstacles to a fully efficient use of storage space in VM disks. By default, the VM disk does not shrink when files are deleted in the guest operating system. In addition, many guest operating systems always direct new writes to free disk blocks. This can cause a small file that is frequently written to, such as a log file, to grow to consume a large amount of disk space.
The guest operating system can send TRIM/UNMAP commands to allow the virtual machine disk to reclaim previously used space as free disk space.
By default, support for these commands is not enabled. To request that this feature be enabled for your SDDC, contact your VMware account team. The feature is enabled on a per-cluster basis. You must reboot the workload VMs in the cluster to allow them to take advantage of this feature after enablement.
When deleting large files or performing a scheduled space reclamation job to reclaim a large block of capacity, the space reclamation process can affect production workloads. This most often manifests as increased latencies. If possible, schedule large space reclamation jobs during off-peak hours to reduce any potential impact. After it has caught up, the system can process in-line deletes without incurring significant penalties.