i bought My cloud ex 2 ultra with 8tb storage listed on the box, but it only appear 4tb in mycloud, how do i change it to 8tb?
By default your device will be in RAID1 mode, so your 8TB is being used to write everything twice. Basically you have 2x4TB drives in the EX2, and in RAID1 mode each file is written automatically to both drives so they mirror one another. If one drive fails, you then still have the data on the other and it can be accessed normally (and when you replace the broken drive, the array can be rebuilt).
If you want full 8TB, you need to switch the EX2 to another mode (JBOD, RAID0 or spanning, I’m not sure what the EX2 offers). But if you do that then you obviously won’t have the mirroring functionality, if you lose a drive then the data on it (and potentially all of your data if you choose spanning or RAID0) will be lost.
Note switching between modes will completely reformat all of the drives involved, and all data on them will be lost.