[OpenIndiana-discuss] Formula raidz storage space caclulation

[PÁSZTOR György]

Hi,

"Randy S" <sim.ple at live.nl> írta 2014-04-08 17:05-kor:
> 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? 
You are wrong, where round "up" instead of down when you count "27TB"
"27 TB" mean 27TiB "Usable" bytes, which is 27*10^12 bytes.
That you divide with 1024, and get kilos,
that you divide with 1024 to get mega,
that you divide with 1024 to get giga.
So, if you type in this:
pasztor at daedalus:~$ echo -e 'scale=1\n27*10^12/1024^3' | bc
25145.7

You get the same results.

Regards,
György