@saketb
I assumed ReadyNAS will do the job for formatting it into BTRFS before creating new volumes. I could be wrong. Which link you have referred in your post?.
I have copied the content of the PDF file from ReadyNAS website for you. Kindly follow the below steps one by one to get the drive formatted properly. Link to pdf... http://www.downloads.netgear.com/files/GDC/READYNAS-100/ReadyNAS%20OS%206%20Desktop_IG_12Jun2013.pdf
Reformat Disks
If you are using previously formatted disks that contain data, you must reformat the disks before you can use them with your ReadyNAS system.
Warning: This process erases all data and reformats all disks into a single X-RAID2 volume. If you want to preserve the data on the disks, you must back up the data to an external drive before using the disks in your ReadyNAS storage system.
To reformat previously formatted disks:
1.If your system is powered on, gracefully power off the system.
See Additional Information on page 9.
2.Install the previously formatted disks.
For a list of supported disks, see the Hardware Compatibility List at Hardware Compatibility List Hard Disks.
For information about installing disks, see the hardware manual for your system.
3.Using a straightened paper clip, press and hold the Reset button.
4.Press the Power button.
The system powers on.
5.Continue pressing the Reset button until the system enters boot mode.
If you have a 2-bay storage system, the Power, Disk 1,
Disk 2, and Backup LEDs light when the system is in boot mode.
If you have a 4-bay or 6-bay storage system, the status display screen indicates that the system is in boot mode.
8
6.Select the factory default option from the boot menu.
If you have a 2-bay storage system, do the following:
aScroll through the boot menu options by pressing the Backup button.
bWhen only the Disk 1 LED is lit, press and release the Reset button.
If you have a 4-bay storage system, do the following:
aScroll through the boot menu options by pressing the Backup button.
bWhen the status display screen shows the factory default option, press and release the Reset button.
If you have a 6-bay storage system:
aScroll through the boot menu options using the arrows on the touchpad.
bWhen the status display screen shows the factory default option, press the OK button.
The system initiates a short disk test that takes 2 to 5 minutes.
Then, a 10-minute time-out period begins. After 10 minutes, the factory default process starts.
7.(Optional) Press the Backup or OK button to skip the 10-minute time-out period and begin the factory default process immediately.
The system returns to its factory default settings and reformats all installed disks for use with ReadyNAS OS 6.
When the factory default process is complete, the reformatted disks are ready to use with your system.