QNAP NAS

Procedures

This can be achieved purely through the web interface...

Insert new disk
Format the disk through Disk Management > Volume Management (takes 30 mins or so for a 1.5TB drive in a TS-410)
Expand the RAID volume through Disk Management > RAID Management (takes around 4 days to expand 3 -> 4 x1.5TB drives on a TS-410)

...but it is painfully slow, and for safety its recommended that you limit IO through your device whilst its in progress.

Check out the forum, there's a quicker command line method, which takes your device offline whilst the expansion takes place.

Assuming the device is completely inaccessible (either via the web GUI or SSH), try the following...

Remove all disks
Restart the system
After a while detect the system using QNAP Finder (it'll have lost its config so will need to obtain a DHCP address)

Obtain the latest firmware image, use the following URL's as a guide, and work out the current version from http://www.qnap.com/download.asp...
Power of the NAS
Remove all the HDDs
Power on the NAS
After a short beep and a long beep(about two minutes after first short beep), run the QNAP Finder(Make sure the Finder is the latest version).
QNAP Finder should find the NAS and its IP
Select the NAS and click Tools -> Update Firmware
Input default username and password (admin/admin)
Follow the page to select the firmware file (the flash image file which is about 13MB to 14MB).
After firmware update, the NAS will be reboot.
Make sure the firmware have been updated
Power off the NAS
Plug all the HDD back
After power on, Update the firmware again using the update image on QNAP download site( which is about 90MB to 100MB).