"Yes" - Writes to the server are done asynchronously. When your NFS client sends a write request to an NFS server, the server returns a positive response to your client before writing any data to its disk. Your client can then send another write request without waiting for the server to complete the previous write. Write performance is better with asynchronous writes than with synchronous writes. However, if the server crashes after sending the positive response to the client but before writing the data to disk, the data is lost, and the client is not notified.

"No" - Writes to the server are done synchronously. When your NFS client sends a write request to an NFS server, the server writes the data to its disk before returning a positive response to your client. Your client must wait until the server writes the data to disk before it can send another write request. Write performance is not as good with synchronous writes as with asynchronous writes.

The default is "No".