I'm on Firmware 1.6. it has been happening over a few different firmware versions. I set up the email notification and I recieved a lot of emails before the NAS shutdown. Below is one of the emails i Recieved
DISK Error Notification
HDD error occurred
Disk(s) the error occurred:"Disk 2"
(sdb) WRITE sector:14010472 count:6
Disk writing error
Some data may not be recoverable.
Immediate change of disk is recommended.
And another email was
DISK Error Notification
HDD error occurred
Disk(s) the error occurred:"Disk 2"
(sdb) WRITE sector:14012760 count:7
Disk writing error
Some data may not be recoverable.
Immediate change of disk is recommended.