Volume degraded, however resync completed

Duplicate Post - this thread can be deleted - thanks

running 6.8.1 on a RN212, XRaid1, Raid 1

I was upgrading my drives from 4tb to 6tb.  I took out drive 2, put in the new 6tb drive and left it to do it's thing.  11 hours later, it had finished copying 3.17tb, so I put in the new 6tb drive in drive 1.

The new drive 1 finished copying everything back ,  and I got the message that says's "Volume data health changed from Degraded to Redundant."

After getting 15 'ATA Error count increasing' messages (which finished at 1647).  Now it says resyncing complete, but the volume is degraded.

Does that mean the drive is bad?  

Can I continue to run on the good drive till I get a replacement?

or Should I put my old 4tb back in drive 1?

Drives are Toshiba N300 HDWN160