It depends on your personal need / storage pool size.
I would prefer 2-bay x 2. But buying at different timing (coz 2-bay is good enough for my current usage). As such, I can get another 2-bay sometime later, having newer/higher hardware spec.
If 4-bay is your immediate need, it seems getting a 4-bay nas is much better.
我就咁分析,
raid5 就廢既,
raid6 4bay又唔抵,
最重要係
btrfs parity RAID should not be used for anything other than testing purposes.
ref: https://btrfs.wiki.kernel.org/index.php/RAID56
簡單D講 你得返 raid 1 揀
raid 1只要死淨一隻就得
只要2 WAY mirror就足夠
如果你2-way都可以死晒, 多數都天災人禍, 10-way mirror都收皮
2 x 2 可以physically分開放, 希望天災人禍 果時, 可以生存一隻
sorry, 我都未知你個用途,
我淨係從安全角度諗野, 如果d data唔係太重要就梗係1 X 4