How to flush cache of certain disk?

[Alexander Batischev <eual.jp@gmail.com>]

Hi,

On my netbook I'm using automatic USB sticks mount through udev rules,
and I already used to running 'sync' command before unplugging stick,
so no data will be lost. But if I have few sticks inserted and some
information copying on one of them, if I run 'sync' I have to wait
while copying ends, because:

a) sync command drops cache on disk, but copying process fill it
again; sync will work until all the caches are dropped to disks
b) I can't unplug stick when it stops to flash because I can't be sure
that there are no more parts of cache needed to be flushed on that
disk.

So here is my question - how can I run sync for only one device?

With best regards,
Alexander Batischev