If I use raidZ2, I will lose three disks of space

[bigfly]

12x8T(7.28) raidz 11X7.28=80.08
When I create it successfully, the storage space is only 75.15T

More exaggerated If I use raidZ2, I will lose three disks of space
12x8T(7.28) raidz 10X7.28=72.8
When I create it successfully, the storage space is only 64T
why？

 

[kherr]

An rz1 with 12 disks isn't all that good of an idea .......

https://wintelguy.com/zfs-calc.pl and play with the #'s, there's various ZFS overhead to consider.

With a convectional raid array you take the # total disks less redundant # of drives times "advertised" size times .9 to get an approximation. ZFS has less than that. the calculator will tell all.

 

[Constantin]

Besides whatever parity losses there are, ZFS pools also should not be filled above 80% capacity or ZFS performance will degrade significantly.

For my eight drive Z3 setup, that means 3 drives worth of capacity is lost to parity, and another to the 20% headroom, leaving me with 4 drives worth of data storage capacity.