QNAP 453BT3 adding one bigger drive to Raid 5

[ishootraw78]

Hello guys, new to this forum.
I have a qnap 453BT3 (thunderbolt) with 4 HDD of 4tb each.
I have a warning that its almost full so I ordered one 18 tb HDD and swapped the first drive, thinking that I would have more storage. but it stays the same. I followed a YouTube tutorial, replace disk one by one but after the rebuild I can't choose expand capacity.
Is one hdd not enough, and I need minimum 2? Or did I do something wrong?
thank you so much.

[Kunzite]

Bad news: you need to replace all the HDDs in the RAID array you want to expand.

[Barungar]

Simple rule... the capacity of a RAIDx (1, 5 or 6) is always determined by the size of smallest drive present.
You'll need to remove all 4 TB drives and replace them with something bigger.

In your case the RAID is still three 18 TB drives short.

[ishootraw78]

that ** but thanks guys

[Barungar]

That's the way it works... Of course you don't need three additional 18 TB drives. You could also use three 6 TB drives but than 12 TB of your 18 TB drive will be wasted. At the moment 14 TB of your new drive are wasted.