[OpenIndiana-discuss] Formula raidz storage space caclulation

[Randy S]

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? 

Thanx

R

> Date: Tue, 8 Apr 2014 16:32:23 +0200
> From: pasztor at linux.gyakg.u-szeged.hu
> To: openindiana-discuss at openindiana.org
> Subject: Re: [OpenIndiana-discuss] Formula raidz storage space caclulation
> 
> Hi,
> 
> "Randy S" <sim.ple at live.nl> írta 2014-04-08 16:16-kor:
> > The information that I have about the formula to use is (n-1) x storage space per disk
> > n=number of disks 
> > 1=is de disk used for parity in a raidz1 configuration.
> > In the case of Raidz2 , this number would be 2 (n-2) x space.
> > 
> > My question is: is this formula correct?
> > Reason, my outcome always differs with from the outcome on the following website: http://www.servethehome.com/raid-calculator/
> > What would be the correct formula to use?
> 
> Did you count in your calculations what the manufacturers cheat on the
> meaning of kilo (1024 vs 1000)?
> They also note that:
> "
> *Usable storage is the actual post-format amount where kilo = 1024, not
> 1000
> "
> 
> Regards,
> György
> 
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