Greetings I have been running a raid 10 array for almost 3 years. Last September on a reboot (forced by Firefox and kernel memory interaction problems) came up with one of the drives being listed as DOA. The raid array has continued to run on 3 drives although on reboots there is much complaining from whatever in the boot up process. I had the replacement drive sent to me and today I installed the drive. I was under the assumption that the raid array would rebuild itself upon startup with a new drive (4th out of 4). This did not happen. I am running Debian Jessie (testing) and have the whole time in question. I can mount the array and it is visible. I'm looking at backing up the array (on blu-ray discs) but as I'm now to circa 45 GB of data and I was at about 22 GB when I last did a backup this is going to be a momentous event. How do I ask mdadm to include this new drive into the array? (Without borking everything!! I have found lots of instructions on how to create but none in an hour of trying different search phrases on how to rebuild or how to cause the array to rebuild itself. I have only been able to find instructions for when the array is totally sick and I'm not there (yet - - - grin!) but I don't want to wait until another drive craps out to get things going.) TIA Dee