Just to add to the confusion: async

[John Andrewartha]

Try this version.
Good English 5 lines and says it all

Cheers John

async

Caution is advised when using this command.
All I/O to the file system should be done asynchronously to
ensuring maintaining the full integrity of the file system.
The use of the 'async' flag by an application may cause unrecoverable
data loose and corrupt the disk beyond recovery.