Out of the box with the RAID you are likely to find an email everyday with the subject similar to:
SparesMissing event on /dev/md/Mirror:nas2 [nas2.cantabrian]
This is a somewhat know error, ssh to the box and look for:
You will probably find a line like:
# definitions of existing MD arrays ARRAY /dev/md/Mirror metadata=1.2 spares=1 name=nas2:Mirror UUID=fa9357c4:46935ec5:ebf94dda:dc66ddc7
You need to change the “spares=1” to “spares=0”. In fact it looks like you can delete “spares=1” altogether.