NAS326 Volume is degraded and No repair button

Dona

Hello,  I've 2 same disk in my nas326 raid1 .  When boot device beep and give me error on screen "Volume1 is degraded go and repair it"   But there is no Repair option. 
I can still access my files. But this error worries me

Mijzelf

Your hard disk listing shows only one disk. So it you indeed have two disks inside, I'm afraid one died.

Dona

i swapped the disks and plug again. after that repair button appeared on menu. So I repair it. And now working normal.