To implement asynchronous NBDSSL, use the new functions

VixDiskLib_ReadAsync

and

VixDiskLib_WriteAsync

in a callback, followed by

VixDiskLib_Wait

, to replace the VixDiskLib read and write functions. In the development kit, see

vixDiskLibSample.cpp

for code examples, following logic for the

-readasyncbench

and

-writeasyncbench

options.

VDDK has had non-public asynchronous APIs since VDDK 6.0, but behavior is different in earlier releases. File transport mode is synchronous in all releases.

Asynchronous read and write

	VDDK 6.0	VDDK 6.5	6.7
VixDiskLib_ReadAsync	Always synchronous.	Same as 6.0.	For HotAdd and SAN modes, same as 6.0 and 6.5. NBDSSL mode is asynchronous if the ESXi host supports asynchronous NBD.
VixDiskLib_WriteAsync	For HotAdd and NBDSSL modes, always synchronous. For SAN mode, the API is asynchronous. A thread handles writes one by one in the back-end, so outstanding I/O is always 1.	Same as 6.0.	For HotAdd and SAN modes, same as 6.0 and 6.5. NBDSSL mode is asynchronous if the ESXi host supports asynchronous NBD, as does ESXi 6.7.