[CentOS] C7 and mdadm

A user's system had a hard drive failure over the weekend. Linux RAID 6. I
identified the drive, brought the system down (8 drives, and I didn't know
the s/n of the bad one. why it was there in the box, rather than where I
started looking...) Brought it up, RAID not working. I finally found that
I had to do an mdadm --stop /dev/md0, then I could do an assemble, then I
could add the new drive.

But: it's now
cat /proc/mdstat
Personalities : [raid6] [raid5] [raid4]
md0 : active (auto-read-only) raid5 sdg1[8](S) sdh1[7] sdf1[4] sde1[3]
sdd1[2] sdc1[1]
      23441313792 blocks super 1.2 level 5, 512k chunk, algorithm 2 [7/5]
[_UUUU_U]
      bitmap: 0/30 pages [0KB], 65536KB chunk

unused devices: <none>

and I can't mount it (it's xfs, btw). *Should* I make it readwrite, or is
there something else I should do?

        mark