Storage & Clustering Community Blog

Written by: Thomas Cornely

What’s the Hardware Zero Reclaim functionality?  It basically refers to the array’s ability to scan a thin lun and look for pages of physical storage that contain ‘all zeroes’. When they find such a page, they reclaim the page (i.e. detach it from the thin lun) and put it back in the free pool. They can do this because the array returns ‘0’ to any I/O read it received on ‘unallocated space’ in a thin lun.

Who’s doing it?

Most hardware vendors are coming out with similar functionality. IBM XIV was the first one to have it. 3PAR has it. NetApp has it (they actually have true dedup in the array). Now Hitachi has it.

What are limitations of the Hardware Zero Reclaim functionality?

Hardware Zero Reclaim relies on the presence of 0 in the array to do the reclamation. In the context of a thick to thin migration, the process would be as follows:

• start with 1...