My server is set up with raid1. A few nights ago sda fell out completely and data was corrupted. I replaced the drive, cloned the partition table and added the respective arrays. While adding sda3 (MD2) the resync kept failing due to sdb having I/O errors. I copied all the files I could save from sdb3 to sda3, reconfigured raid and replaced sdb with a new drive. I'm now adding the sdb partitions to the arrays. My concern is as follows:
cat /proc/mdstat Personalities : [raid0] [raid1] [raid6] [raid5] [raid4] [raid10] md3 : active raid1 sda4 1822442815 blocks super 1.2 [2/1] [U_] md2 : active raid1 sda3 1073740664 blocks super 1.2 [2/1] [_U] md1 : active raid1 sdb2 sda2 524276 blocks super 1.2 [2/2] [UU] md0 : active raid1 sdb1 sda1 33553336 blocks super 1.2 [2/2] [UU]
Both md0 and md1 displayed as [U_] prior to syncing, why would md2 display as [_U]? I fear losing the data when adding sdb3. My thinking here is the the first slot ([U_]) is seen as primary by mdadm and the second slot ([_U]) as secondary hence the fear of the data being removed to match sdb3.