QNAP RAID and back to same disk sizes

[hybraq]

Hello
I configured a TS-453b in RAID5 with these disk sizes:
5TB,4TB,4TB,4TB
So far so good, but now I would like to swap the 5TB with a 4TB, so that I don’t waste a 1TB. Is it possible? I keep reading that when you hot swap a disk in a RAID array the newcomer should be same or larger size, but in my case I my understanding is the 1TB of the disk1 wasn’t being used anyway.
Asking this because I already tried to do the operation (swap the 5TB for a new 4TB) and I got “not a member” for the new disk (a WD RED pro, the old ones are HGST), and the array rebuild wasn’t being started. Is it possible this new disk came dead on arrival or what I am trying to do is just not allowed by this NAS? (5TB+4TB+4TB+4TB to 4TB+4TB+4TB+4TB)

[dolbyman]

Have you opened a ticket yet ? When you posted this a couple of days ago, that was the advice. So why post that question now 2 more times ?

viewtopic.php?f=25&t=165324&p=818522#p818522

[hybraq]

I posted for the public to find an answer to a specific question in the future, since I was not the OP of the thread I replied before and that issue was different. Support tickets are not searchable by the public.
Anyway yes, I opened a ticket too.

[hybraq]

I tried now to do the same with a new 4TB WD RED PRO disk (identical to the previous I tried) and this time the RAID rebuild started.
So it seems it is possibile to downgrade a drive to the lesser size, if it is at least the size of the smaller in the array. My previous disk was probably defective, as detected by the Storage & Snaphot panel.