QNAP TS-459 Pro II, firmware version 4.2.6 (26.10.2017)
Raid 5 configuration with 4 disks.

Few days ago my QNAP made a warning sound and reported disk 1 for faulty, and the disk array went into “degraded mode”. My raid 5 consisted of 4 x 2TB Seagate Constellation (ST2000NM0033) HDD drives. Two of the drives (actually disk 1 and disk 2 in the array) showed seriously bad numbers in the S.M.A.R.T test, so I decided to change the whole array as soon as possible.

I decided to buy the Western Digital RED WD30EFRX drives with a capacity of 3TB but worried about the QNAP’s ability to firstly replace the disks in the array and secondly expand the array from initially 5.5 TB (the resulting capacity of 4 x 2TB [1863GB]) to 8.2 TB (the resulting capacity of 4 x 3TB [2794GB]).
Don’t worry, It all worked out just perfect, using the admin interface.

0) Disable any “restart/shutdown” schedule before you start messing with your raid configuration or rebuilding disk images.
1) First confirm that the System light on the front of the QNAP is blinking red (it is normally steady green). In the admin interface – “System interface – Storage manager – Volume management”, the “Current configuration: Logical volumes” will state “in degraded mode”.
2) With the system turned on, do a hot swap of the faulty disc, meaning; remove the disk and wait for the system to beep twice. The QNAP will show “Disk n removed” in the display, and in the admin interface, “Current configuration: Physical Disks” will show that the bay is empty. “Current configuration: Logical volumes” shall still state “in degraded mode”.
3) Insert a new disk and wait for 30 secs – 1 minute. The disk should be correctly identified and “Current configuration: Logical volumes” will state “Rebuilding”. The rebuild of the raid array took approx 9 hours in my case.

Now go on and change the rest of your discs, one at a time, by removing the next drive in your array – insert a new disc – rebuild (follow step 2 and 3). When rebuild is finish change the next disc…

When all four discs has been changed, it is time for doing the Expansion. At this point of time “Current configuration: Logical volumes” will state “Ready”. Go to “System interface – Storage manager – RAID management” and press the volume you want to expand (Raid 5 Disk Volume: Drive 1 2 3 4) and then press the button “Action”.
Choose “Expand capacity”.
The system will stop all services and afterwards inform you about the maximum array size. Choose “Expand” for the process to start. This process took approx 30 minutes to complete on my system.

Remember to enable “bitmap” when the expansion is finished. This can be done in “action”-button menu too.
You should be all good when the process finish and your system should reflect the correct new capacity.

Disclaimer: I accept no responsibility what so ever, for the resulting effect on your system – This worked perfect for me, but any damage and/or loss of data is your own responsibility. Sorry you are on your own.