Thanks,i got it. But i have another question.Sometimes, i can't remove the device, in the "dmsetup man", it said "because an uninterruptible process is waiting for I/O to return from it", and what should i do for getting the PID or something about this "uninterruptible process"? I know adding "--force" can help me remove the device, but i am worried about this action will cause I/O broken. <div class="gmail_quote">On Mon, Jan 17, 2011 at 11:29 AM, Alasdair G Kergon <<a href="mailto:agk@redhat.com">agk@redhat.com</a>> wrote: <blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"> <div class="im">On Mon, Jan 17, 2011 at 10:12:51AM +0800, tom z wrote: > What's the meaning of the "Event number". Is it number of the device's > I/O event? If the number is greater to zero, it means the I/O request's > happening? </div>No. Just means something happened that userspace ought to know about, like a path failing. Used by 'wait' - see 'man dmsetup' and <a href="http://people.redhat.com/agk/talks/FOSDEM_2005/text51.html" target="_blank">http://people.redhat.com/agk/talks/FOSDEM_2005/text51.html</a> . Alasdair </blockquote></div>