F on one raid 1 device degraded raid

Hello,

I found out that the raid 1 was degraded:

[rootnode /]# cat /proc/mdstat
Personalities : [raid1]
md3 : active raid1 sda5[0] sdb5[1]
1822445428 blocks super 1.0 [2/2] [UU]

md2 : active raid1 sda3[0](F) sdb3[1]
1073741688 blocks super 1.0 [2/1] [_U]

md1 : active raid1 sda2[0] sdb2[1]
524276 blocks super 1.0 [2/2] [UU]

md0 : active raid1 sda1[0] sdb1[1]
33553336 blocks super 1.0 [2/2] [UU]

so it seems to me that in partition md2 the device sda3 was Faulty.

so I did try to remove and re-add it in order to repair it:

[rootnode /]# mdadm --remove /dev/md2 /dev/sda3
mdadm: hot removed /dev/sda3 from /dev/md2

then I tried to add it again:

[rootnode /]# mdadm --add /dev/md2 /dev/sda3
mdadm: /dev/sda3 reports being an active member for /dev/md2, but a --re-add fails.
mdadm: not performing --add as that would convert /dev/sda3 in to a spare.
mdadm: To make this a spare, use "mdadm --zero-superblock /dev/sda3" first.

and the result is:

[rootnode /]# cat /proc/mdstat
Personalities : [raid1]
md3 : active raid1 sda5[0] sdb5[1]
1822445428 blocks super 1.0 [2/2] [UU]

md2 : active raid1 sdb3[1]
1073741688 blocks super 1.0 [2/1] [_U]

md1 : active raid1 sda2[0] sdb2[1]
524276 blocks super 1.0 [2/2] [UU]

md0 : active raid1 sda1[0] sdb1[1]
33553336 blocks super 1.0 [2/2] [UU]

unused devices: <none>


so

md2 : active raid1 sda3[0](F) sdb3[1]
1073741688 blocks super 1.0 [2/1] [_U]

changed to

md2 : active raid1 sdb3[1]
1073741688 blocks super 1.0 [2/1] [_U]

and I cant re-add the 2nd device,
If I run mdadm --zero-superblock /dev/sda3
would what erase my data from the partion? or would that create any other damage?

I've searched the manual which says:

--zero-superblock
If the device contains a valid md superblock, the block is overwritten with zeros.
With --force the block where the superblock would be is overwritten even if it doesn't appear to be valid

but i;m not sure if this erases data and since the partition mounts to / in which all the data is, i'm scared to tried it without verification.

If anyone knows that would be really helpfull.

after lots of research I decided to go on with it

[root@node ~]# mdadm --zero-superblock /dev/sda3
[root@node ~]# mdadm /dev/md2 -a /dev/sda3
mdadm: added /dev/sda3

[root@node ~]# cat /proc/mdstat
Personalities : [raid1]
md3 : active raid1 sda5[0] sdb5[1]
1822445428 blocks super 1.0 [2/2] [UU]

md2 : active raid1 sda3[2] sdb3[1]
1073741688 blocks super 1.0 [2/1] [_U]
[>....................] recovery = 1.1% (12009408/1073741688) finish=313.7min speed=56397K/sec

md1 : active raid1 sda2[0] sdb2[1]
524276 blocks super 1.0 [2/2] [UU]

md0 : active raid1 sda1[0] sdb1[1]
33553336 blocks super 1.0 [2/2] [UU]

as you can see the result is the raid is recovering so everything is ok and --zero-superblock didn't damage any data.