You can only perform thin storage reclamation on LUNs that have the thinrclm attribute. An array may be a good candidate for reclamation if:
Your array-specific commands indicate that storage is nearing the maximum; for example, 90% is used.
You receive an alert from the array that a certain storage level has been reached.
Even if storage capacity is reaching the maximum, that does not necessarily mean there is any data to reclaim; the data could still be needed. You should investigate further to determine if there are large blocks of deleted or unused data. If there are, run thin reclamation.
For more information reclaiming storage, see Symantec Storage Foundation and High Availability Solutions Solutions Guide.