RAID 1 Issue - Volume Degraded after HDD replacement

I hava ReadyNAS 104 with  firmware 6.6.1. Inside it I had 1 TB, 1TB, 3 TB and 6 TB HDDs, the two first configured as RAID 1.

I had a RAID 1 with 2 HDD of 1TB, but one of them stop working. While I receive a new one, a replace the broken one with a 2 TB HDD (I know I'm loosing 1 TB of space).

It was detected as part of the RAID 1, and started syncronizing. After it was sincronized, the HDD status change from SYNC to ONLINE, but the volume status is DEGRADED.

I  think the problem is that the 2 TB HDD is set as SPARE instead of ACTIVE SYNC. If you get the raid detail you see that there are 2 working devices, but only 1 active devices. As you can see, the status is clean,degraded.

# /sbin/mdadm --detail /dev/md125
/dev/md125:
Version : 1.2
Creation Time : Thu May 28 13:29:45 2015
Raid Level : raid1
Array Size : 971912832 (926.89 GiB 995.24 GB)
Used Dev Size : 971912832 (926.89 GiB 995.24 GB)
Raid Devices : 2
Total Devices : 2
Persistence : Superblock is persistent

Update Time : Tue Apr 25 09:51:21 2017
State : clean, degraded
Active Devices : 1
Working Devices : 2
Failed Devices : 0
Spare Devices : 1

Name : 2fe53622:Personal-0 (local to host 2fe53622)
UUID : e9cdfd26:c97e9f56:51e0ac36:3c2bb179
Events : 116364

Number Major Minor RaidDevice State
0            8        51      0                 active sync /dev/sdd3
2            0        0        2                 removed

1            8        67      -                  spare /dev/sde3

Can anyone help me?