TS5200D - Trying to rebuild RAID with new drive - Drive too small

[talbrecht70]

I have replaced a failed drive and Im trying to rebuild the RAID, but its telling me the drive is too small.  Ive replaced the failed 4 TB drive with another 4 TB drive.  The good drive is 4 TB as well. 
I checked it on diskpart and saw that all the space has been allocated and is GPT.

[Texturtle]

It needs to have no partitions on it and unformatted. You can use diskpart to wipe everything.

https://www.buffalotech.com/knowledge-base/cleaning-a-disk-in-windows-7-using-diskpart

[davo]

I have replaced a failed drive and Im trying to rebuild the RAID, but its telling me the drive is too small.  Ive replaced the failed 4 TB drive with another 4 TB drive.  The good drive is 4 TB as well. 
I checked it on diskpart and saw that all the space has been allocated and is GPT.

Go to Drives - Drives - Select the replacement disk - dismount disk - Once complete select the disk again - Rediscover disk.

The disk should then show as unformatted and you can then recover the RAID.

The issue is that you probably formatted the disk on the Terastation UI, which you shouldn't do.