Apparently once should always leave a bit of empty space at the end of each raid1 partition. But if we're too late for that, what can be done if a replacement RAID1 drive is slightly smaller than the surviving drive?
Can the array be resized to be smaller?
In this case, hdparm shows:
Model=ST31000524AS, FwRev=JC45, SerialNo=9VPBMQJD CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=1953525168
Model=ST1000DM003-1CH162, FwRev=CC44, SerialNo=S1D7LDD7 CurCHS=16383/16/63, CurSects=16514064, LBA=yes, LBAsects=1953525168
But fdisk partitioned the older drive at 976760832 blocks and the new one at 976760001 due to a different logical sector size. There is one partition, formatted ext3.