Dell Unity file systems are built to meet administrators’ changing needs as easily and flexibly as possible. Dell Unity allows for increased flexibility by providing the ability to shrink and extend all file system types. With manual and automatic file system extension and shrink with reclaim, Unity always makes the most efficient use of pool capacity and allows administrators to respond to changing environmental factors including file system utilization, pool utilization, and client capacity demands. Each of these space efficiency operations can be performed or monitored easily through Unisphere, without requiring administrators to meticulously plan file system size changes or perform complex migrations as requirements change. These operations are also fully compatible with replication. Whenever the source file system is manually or automatically shrunk or extended, the replication destination file system is modified to reflect the same total and allocated space after the next sync completes.

It is important to understand the differences between the manual and automatic shrink and extend operations. Manual shrink and extend operations are used to resize the file system and update the capacity that is seen by the client. This is done by updating the Size attribute in the properties of a file system. If a manual shrink operation on a thin file system shrinks into Allocated space, it may be possible to reclaim capacity back to the pool. For manual shrink and extend, the minimum value is equal to the Used size of the file system and the maximum value is 256 TB. You cannot shrink the file system to less than the Used size, as this would cause the client to see the file system with as 100% full.

Automatic shrink and extend operations occur in the background on thin file systems and do not need to be managed by the administrator. Automatic shrink is designed to ensure file systems are efficiently using their allocated capacity. It continuously checks the used-to-allocated ratio on each file system to ensure the amount of allocated capacity is appropriate. If it detects there is too much capacity allocated to the file system that is not being used, automatic shrink triggers a reclaim of that capacity back to the pool so that it can be used for other resources.

Automatic extend is designed to allocate additional capacity to the file system as it is being written to. When a thin file system is first created, very little capacity is allocated to it regardless of its configured Size. As clients write data to the file system, automatic extend allocates additional capacity from the pool to the file system. This ensures there is enough capacity on the file system to absorb incoming writes. Automatic extend operations continue happening until the Size of the file system is reached.