Over the past several months we've talked to storage managers around the world and we have collected some interesting perspectives on how to handle “dead” space on the SAN that we would like to share.
First, let’s define the problem.
Users are deleting files on virtual disks and Windows deletes the file system pointers to the file. While Windows deletes the file nothing is communicated to the storage that the file is no longer valid and the space it occupies should now be free. As a result, the space that the file occupies on-disk is now inaccessible to the storage controller.
Whenever a user deletes a file it adds to the amount of inaccessible (dead) space on the SAN and this space will continue to grow until something is done about it. Storage vendors have built Zero Detection and UNMAP recognition into their hardware to reclaim space, but they have not provided any tools for the identification of the candidate dead space in the guest systems where the problem originates. The decision on what to do on the guest is up to the individual administrators.
To read more, download whitepaper: Managing Your Dead SAN Space Problem: 4 Options, 1 Solution