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ZFS Snapshots
Many of the workgroup and community clusters at UD make use of ZFS to provide storage space. ZFS is a Copy-On-Write (COW) storage technology, meaning that changes are always written to unused blocks in the underlying storage pool rather than overwriting blocks currently occupied by those entities. At any time a snapshot of the file system can be created very quickly and efficiently. Each snapshot references the blocks used at that point in time, and future changes naturally do not affect those blocks (thanks to COW).
The primary caveat to snapshots: they reference (consume) storage pool capacity that would otherwise get reused over time. Thus, it is often necessary to destroy older snapshots to make space available for new changes to the file system (the only other option being growing the underlying storage pool to add new capacity).