The following characteristics are some of the primary benefits of using Consistency Points instead of passing writes directly to disk:
WAFL file system integrity:
Even during a power loss, the WAFL file system remains in a consistent state.
All operations acknowledged by the controller to the clients are confirmed consistent and are preserved intact.
This allows for rapid boot up no matter how the node was taken down since WAFL file system consistency checking is not required.
Increase in client write performance:
Since memory is significantly faster than spinning media, the end client receives faster acknowledgment of its writes and can continue processing the next write request.
A performance gain is also attained on the disk subsystem since the write operations to disk can be grouped together into larger sequential writes instead of many smaller random writes.
Optimized data layout:
Since the writes to disk are processed in bulk, the WAFL subsystem can allocate larger swaths of data in contiguous space on the disk.
This minimizes the possibility of data layout randomization and thus prevents the need for data reallocation.
Decreased requirement for non-volatile RAM (NVRAM) / Memory buffer size:
This is not obvious at first; however, logging write requests as they arrive consumes a considerably smaller amount of memory than would be required if the caching was done after processing by Write Anywhere File Layout (WAFL) and RAID layers.
This also prevents a failure of NVRAM from resulting in a damaged filesystem that normal file system consistency checks cannot detect nor correct.