New disk not recognized in NSA320 at firmware 4.51

Hi,

I wanted to replace the 3TB hard disks with 4TB hard disks in an NSA320 at firmware 4.51 with a RAID1 configuration in OK condition.

After the shutdown and the replacement of disk1 with the new 4TB disk the NAS would not recognize it and would show only disk2 and could not initiate the repair.

I have shutdown again and placed back the previous 3TB disk1 and after the power up the NAS is still showing only disk2 and not able the see the original disk1 anymore.

Any ideas?

Thanks,

Alex