When a thin LUN is used as a Veritas Volume Manager disk, the space is allocated only on an application write. Storage space is allocated from the free pool when files are created and written to in the file system. However, this storage is not automatically released to the free pool when data is deleted from a file system. As a result, all thin LUNs have a tendency to become thicker over time, with increased amounts of wasted storage (storage that is allocated but does not support application data).
As a storage administrator, you need to determine when to trigger the thin reclamation. The thin reclamation process can be time consuming, depending on various factors such as the size and fragmentation of the file system. The decision is a balance between how much space can be reclaimed, and how much time the reclaim operation will take.
The following considerations may apply:
For a VxFS file system mounted on a VxVM volume, compare the file system usage to the actual physical allocation size to determine if a reclamation is desirable. If the file system usage is much smaller than the physical allocation size, it indicates that a lot of space can potentially be reclaimed. You may want to trigger a file system reclamation. If the file system usage is close to the physical allocation size, it indicates that the physical allocation is being used well. You may not want to trigger a reclamation.
The array may provide notification when the storage pool usage has reached a certain threshold. You can evaluate whether you can reclaim space with Storage Foundation to free more space in the storage pool.
Deleted volumes are reclaimed automatically. You can customize the schedule for automatic reclamation.