This is how I did it on my 589 Pro (QTS 4.x) and 873e (QTS 5.x) ...

Just keep in mind: Be patient.
This will go rather slow. For example detecting that a disk is removed, and later a new disk has been inserted, and rebuilding the RAID volume, it all takes time ...
(FYI: I'm not that patient, so I have te remind myself about this whenever I do this as well 😉 )

You do not need to shut down your QNAP but you will need te replace a disk and have it rebuild the RAID volume.
Replace the second disk after that rebuild has completed.

The basic steps are:

1. While the system is running, remove only ONE disk.
2. Wait until QTS reports this disk is missing (it will beep and it should show in the web interface)
3. No place ONE new disk in the system.

Your QNAP will now inform you that a new disk has been placed (takes a minute to detect that) and the volume needs to be rebuild (takes a minute or so before you actually see this in the web interface). Considering that you have 3Tb disks: this may take a few hours.

I cannot stress this enough: be patient, replace one disk, rebuild the RAID volume, then replace the next diks etc.

You can find some QNAP reference materials here.

Hey @hans 

Thx so much for clarifying this. I did came to the same conclusion, one disc at a time the patient thing i was not aware of so good to know.

I did read some people had the problem when the disc was pulled they was never told that and the same when new disc was inset not notification also.

So i'm sure that comes back to the patient thing. Wait until you see every step and the proceed √

I also read about people doing exactly this but after pulling one drive the system showed missing disc or warning of some kind but when new disc was

inserted the rebuilding never started :( and that is the thing i'm afraid of.

But i will try what your saying. Patient, Patient and more Patient....

Thx again buddy 🙏🏻

Yeah, I'll tell you from my experience: Patient is important. When I do these things I'm always nervous of loosing my data.

Goes without saying that a backup is always recommended, but I know that sometimes that is just not a realistic option 😞 
Make sure to make a backup of the most critical things.

Fingers crossed, and I'm confident it will go well.

Note: Way back when I had my QNAP not recognizing the new disk as well.
I just do not know how I fixed it; I think I shut the QNAP down and after reboot it would say the RAID volume was degraded. After that I inserted the disk and the rebuild started just fine.

Sending positive vibes your way ... I know how nerve wrecking this can feel 😉 

Thx again @hans √

@hans 

Forgot to say.

All disc in the NAS now is 3TB disc but the 2 new ones are 5TB RED. But they would still work right ?

That will work, however ... only 3Tb of those 5Tb disks will be used.
Once you replaced all 3Tb disks with 5Tb disks, you can actually expand the RAID volume to use the full capacity.

@hans

Top √

Hey @Hans

One question. The TS-559 Pro II is a 5 bay NAS. When the QTS says Disc 1,2,3,4 and 5 is that from left to right as in a Synology for example ?

So if i want to remove disc 1 that would be the far left. Is that right.

As far as I know (and checked with my 2 QNAPs): disk 1 is to the far left indeed. 😊 

p.s. when you remove one disk, and wait for a bit, de webUI of your QNAP will show what disk was removed.

QTS 4.x on my TS869 Pro show this for the first disk:

Perfect. 

Just changed a disc in my old Synology DS412+ and it went without issue 🙏🏻

Crossed fingers it goes the same with my QNAP TS-559 Pro II

Thx again man

Posted by: @hans

↑

p.s. when you remove one disk, and wait for a bit, de webUI of your QNAP will show what disk was removed.

QTS 4.x on my TS869 Pro show this for the first disk:

-- attachment is not available --

Yeah but it looks like your QTS is later that 4.2.x, mine is still 4.2.6 latests possible :( Looks different.

Or are yours also 4.2.x ?

How you get that photo ?

I hope you mean QTS 😉  (probably a typo)

Anywho ... both my QNAPs start counting disks from the left 😊 

@hans 

Oh yeah ofcause, QTS for sure.

Older QTS i think :