Hello all, I have run into a sticky problem with a failed device in an md array, and I asked about it on the linux raid mailing list, but since the problem may not be md-specific, I am hoping to find some insight here. (If you are on the MD list, and are seeing this twice, I humbly apologize.) The summary is that during a reshape of a raid6 on an up to date CentOS 6.3 box, one disk failed, and was marked as such in the array, but is not allowing me to remove it: # mdadm /dev/md127 --fail /dev/sdg mdadm: set /dev/sdg faulty in /dev/md127 # mdadm /dev/md127 --remove /dev/sdg mdadm: hot remove failed for /dev/sdg: Device or resource busy And in dmesg, I get an error like so: md: cannot remove active disk sdg from md127 ... More details, including mdadm -D output and other diagnostics, are at http://www.spinics.net/lists/raid/msg41928.html . As I note there, the array seems fine otherwise, but is not currently in active use (so perhaps my options are greater than if I wished to keep it deployed). As the other messages in that thread show, I think I've already done the ''obvious'' steps to try to remove the device from the array. Checking things out further, I found that it may be that udev did not completely remove the disk, even though the controller no longer believes that the exported unit exists. (udevadm output is here: http://www.spinics.net/lists/raid/msg41950.html ) So my hypothesis is that if I can somehow force udev to drop the references to the disk completely, perhaps I can remove sdg from the array and start a rebuild with the spare already available. I found these docs for Fedora: https://docs.fedoraproject.org/en-US/Fedora/14/html/Storage_Administration_Guide/removing_devices.html But of course I can't do step 3, since md is refusing to give up sdg. But sdg is already gone, so I really don't care about outstanding IO, and it's a bit too late to worry about a 100% clean removal. So my questions are, will step 7 actually clean up references to sdg, and how likely is it that doing so would let me remove it from the array? And finally, if the above is not a wise way to go, are there better things to try? If other diagnostic output is desired please let me know. Thanks! --keith -- kkeller at wombat.san-francisco.ca.us