I kept getting this strange error from my NAS. A google search led me to a solution on OMV forums.

This is an automatically generated mail message from mdadm running on oracle

A SparesMissing event had been detected on md device /dev/md/oracle:storage1.

Faithfully yours, etc.

P.S. The /proc/mdstat file currently contains the following:

Personalities : [linear] [multipath] [raid0] [raid1] [raid6] [raid5] [raid4] [raid10]
md127 : active raid5 sdb[0] sda[3] sdc[1]
976770048 blocks super 1.2 level 5, 512k chunk, algorithm 2 [3/3] [UUU]

unused devices:

I had to leave a note as I was very thankful that SerErris took the time out to document the fix. Kudos man!

OMV Forums

Thank you documenting this fix. I was having the issue as well. What is strange is that I did not configure a spare. I had a failed hard drive and after I replaced it and rebuilt the array I started getting these alerts.