> I need to suspend the current I/O on my file system.

If you use LVM, you can do:

dmsetup suspend /dev/mapper/logical-volume

and then resume:

dmsetup resume /dev/mapper/megathecus-backup2

> Is there any mechanism to figure out the number of I/O currently happening in > the system?

iostat

> Is there any mechanism to suspend all the current I/O(write) momently on the > file system?

dmsetup suspend/resume - if you use LVM.

> Also,any mechanism to flush all the I/O currently executed in the file system?

Do you mean "sync"?