[OpenIndiana-discuss] Formula raidz storage space caclulation

[Jim Klimov]

On 2014-04-08 17:05, Randy S wrote:
> Hi,
>
> yes even if you incorporate the kilo=1024
> example:
> I filled in the example below on the site:
> RAID Mode: z1
> Disk Size: 3 tb
> Quantity of Disks: 10
>
> RAID-Z
> *Raw Storage: 30.0 TB / 30000.0 GB
> *Usable Storage: 24.6 TB / 25145.7 GB
> RAID-Z uses one disk for Parity much like RAID5 and requires at least three drives to be used.
> *Usable storage is the actual post-format amount where kilo = 1024, not 1000
>
> If I use the (n-1)formula this would amount to:
> (10-1) * 3 TB = 27 TB (27000 GB)
> even if you use 1 TB=1024 GB:
> (10-1) * 3072 GB = 27.648 GB
>
> Somewhere theres about 2.5 TB being used for something in their calculations.
> Maybe someone can explain or show me where my calculation is going wrong?

1024 vs 1000 is another way around: a 3TB disk is
3000000000000 / 1024 / 1024 / 1024 / 1024 = 2.72Tb  or
3000000000000 / 1024 / 1024 / 1024 = 2793.97Gb

Times 9, and that amounts to 24.55Tb or 25145.7Gb

(I am sometimes confused by "b" vs. "B" in such decimal vs. binary
notations, so maybe that should have been written another way around)

HTH,
//Jim