Dell EMC Metro node 7.1 Administrator Guide

Rebuilds for thin provisioned storage

Thin provisioning allows storage to migrate onto a thinly provisioned storage volume while allocating the minimal amount of thin storage pool capacity.

Thinly provisioned storage volumes can be incorporated into RAID 1 mirrors with similar consumption of thin storage pool capacity.

Metro node preserves the unallocated thin pool space of the target storage volume in different ways that are based on whether the target volume is thin-capable or not. For thin-capable volumes, if the source leg indicates zeroed data, metro node issues UNMAP for those blocks on the target volumes. For non thin-capable target legs, metro node checks for zeroed data content before writing, and it suppresses the write where it would cause an unnecessary allocation. For this thin rebuild algorithm to be selected, metro node automatically sets the thin-rebuild flag on thin-capable volumes as part of the claiming process. For the storage volumes not supported as thin-capable, the metro node administrator sets a third property, the thin-rebuild attribute to true during or after the storage claiming.

Metro node allows you to change the thin-rebuild value for storage volumes regardless of whether the storage volumes are thin-capable or not. For thin-capable storage volumes, if you try to set the thin-rebuild property to false, the VPlexcli displays a warning. In a scenario where all the contents of the source are written to the target, performance might be better than the normal rebuild if:

• The storage volumes are not thin-capable
• The contents of the source and the target of the rebuild are almost the same
• Only the differing data is written during the thin-rebuild process

The discovered thin provisioning property of storage volumes enables the creation of thin provisioning capable metro node virtual volumes to which hosts can send UNMAP commands to free the unused blocks. However, the configured thin-rebuild property controls the mirror synchronization that is performed at the metro node back-end.

Thin support in metro node provides you more information on the thin-aware capabilities of metro node.