Dell Unity: What does "Pool is oversubscribed" mean (User Correctable)

Oversubscription is a storage provisioning method that allows storage administrators to provision more capacity than may be physically available in a particular storage pool. This can be useful in situations where users are not expected to use up all the storage allotted to them. Oversubscribed storage pools must be carefully monitored, so that they do not run out of physical space. The pool in this screenshot is at 202.5% subscription, meaning that all the storage resources for the pool have been told that there is 102.5% more space than physically available. There are two ways that a pool can become oversubscribed, use of thin provisioning and snapshots.

Thin provisioning
When you create a thin provisioned 5 TB storage resource, you are essentially telling that resource it is allowed to grow up to 5 TB in size. Instead of reserving the 5 TB up front, storage space is allocated based on actual usage. Through thin provisioning you can create five 5TB LUNs even though you only have 20 TB of physical space. In this case, the subscription for the pool would be 125% meaning that you have told your storage resources that they are allowed to grow up to 5 TB more space than is physically available. When the collective amount of storage used by these LUNs begins to approach the pool's physical capacity, Unisphere generates notifications that more storage is soon required. At this point, more disks have to be purchased and/or assigned to the pool. The hosts connected to thin provisioned storage resources are unaware of the oversubscription. And only see the subscribed size for each storage resource rather than the allocated size.

Snapshots
A snapshot only contains the data that has changed since the last snapshot was taken. When configuring snapshots, space is subscribed from the pool in the amount necessary if the maximum space for each snapshot is required. For example a snapshot of a 5TB LUN might only contain 300GB of data, but the full 5TB is subscribed from the pool.