technical quastions about compability
I want to know before buying the NAS WD My Cloud EX2 Ultra (diskless)
1. If the power goes off and on again, are all settings become disturbed or are setting have to do again?
(because one of the users experienced this issue)
2. I have 2.5 SATA HDD, can I use it by using 3.5 HDD adapter in the bay?
3. In future can I use SSD by using 3.5 to 2.5 Adapter?
4. Can I use only one bay only instead of two bays? (RAID not required)
If the power goes down you do not loose settings. If this happens, NAS might have been in the middle of firmware updates. It is recommended to have UPS for locations with unreliable power. Here are the cheapest ones with a smart interface: https://nascompares.com/cheapest-ups-for-synology-qnap-nas/
You can surely use 2.5 inch SSD inside 3.5inch HDD bays. It has the same connectivity. And in fact this will massively boost your NAS performance. You can use an adapter to or often you get some NAS models with adaptable trays. With EX2 you will need an adapter tray.
Startech is doing adapter like this:
And finally you can start with just a single disk and add another later. Just make sure you have a backup in place.