For large heavy-used jfs2 file system,
it will take long time to umount it.
But if you manually run "sync" before umount,
you will find the total time of "sync+umount" is much less than umount merely.
But theoretically both syncd and umount itself will do same work as sync.....
Why does sync has better performance?
The reason is that sync will use multi-threads when it update "dirty" data of jfs2 file system.
But syncd just use one thread for... [More]