Let me man that for you:

nfs(5)

The sync mount option

The NFS client treats the sync mount option differently than some other file systems (refer to mount(8) for a description of the generic sync and async mount options). If neither sync nor async is specified (or if the async option is specified), the NFS client delays sending application writes to the server until any of these events occur:

• Memory pressure forces reclamation of system memory resources.
• An application flushes file data explicitly with sync(2), msync(2), or fsync(3).
• An application closes a file with close(2).
• The file is locked/unlocked via fcntl(2).

In other words, under normal circumstances, data written by an application may not immediately appear on the server that hosts the file.

If the sync option is specified on a mount point, any system call that writes data to files on that mount point causes that data to be flushed to the server before the system call returns control to user space. This provides greater data cache coherence among clients, but at a significant performance cost.

Единственный параметр, который следует указать — это sync или async (рекомендуется sync). Если вы указали sync, сервер не бедт отвечать на запросы раньше, чем запрошенные изменения будут записаны на диск.

async — это default. сам решай: медленно, но консистентно (sync) или быстро и не чуть-чуть не так консистентно (async). для большинтсва nfs задачь (mostly read) async педпочтительней.

ok