Space Management Considerations

Several operations, such as removing or overwriting a file, can fail when a file system containing Storage Checkpoints runs out of space. Usually these operations do not fail because of insufficient space on the file system, but these operations on a file system containing Storage Checkpoints can cause a data block copy that, in turn, may require extent allocation. If the system cannot allocate sufficient space, the operation will fail.

Database applications usually preallocate storage for their files and may not expect a write operation to fail. If a file system runs out of space, the kernel automatically removes Storage Checkpoints and attempts to complete the write operation after sufficient space becomes available. The kernel removes Storage Checkpoints to prevent commands, such as rm (see the rm(1) manual page), from failing under an out-of-space (ENOSPC) condition.

The kernel will follow these policies when automatically removing Storage Checkpoints:

• Remove as few Storage Checkpoints as possible to complete the operation.
• Never select a non-removable Storage Checkpoint.
• Select a nodata Storage Checkpoint only when data Storage Checkpoints no longer exist.
• Remove the oldest Storage Checkpoint first.