WD my Cloud PR4100 RAID 5 inquiry

Hello, I try to setup my NAS device WD my cloud pr4100, I have 4 TB *4 drives
As I know if I use RAID 5 it will use the 3 volumes and disk 4 could be used as hot spare, so I will have the capacity of 12TB to use + 4TB as hot spare
“the above is also clear in the manual that in RAID 5 it uses quarter of each hard disk”

BUT while I’m setup the device to be RAID 5, it shows me that Volume 1(1,2,3,4) are = 12TB, and if I check mark to use the “spare” option the volume changes to be (1,2,3) and the capacity become 8tb only ??

any one can explain to me where I go wrong !!!

Raid 5 needs at least 3 disks. The size will be 1 less then what you put in.
Your case you said you had 4 disks of 4TB. So 16-4 = 12TB then you took out one drive to be a HOT SPARE. that drive will sit there and do nothing until needed for a rebuild of a defective drive. And won’t be counted.
So your new number as a raid 5 is 3 drives. 12-4 = 8TB.

Raid 5 does not use a “quarter”(well it would if you have 4 drive in raid 5) but it really uses one whole drive in total. If you have 3 drives it uses a 1/3 of each drive. if you have 6 drives it uses a 1/6 of each drive.

I would set it up as a Raid 10. But If you really need the 12TB and need the extra security of the Hot Spare then just buy a extra Hard Drive so if one dies you can put it right in.


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