[OpenIndiana-discuss] Formula raidz storage space caclulation

[Peter Tribble]

On Tue, Apr 8, 2014 at 4:05 PM, Randy S <sim.ple at live.nl> 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?
>

You've converted the wrong way. Your "3TB" drive is really 3000000000000
bytes or 3TiB.

If you correct for the 1024 vs 1000, (with a terabyte, that happens 4
times) you
lose ~10%, which is about what you're seeing.


> 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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> > OpenIndiana-discuss at openindiana.org
> > http://openindiana.org/mailman/listinfo/openindiana-discuss
>
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>



-- 
-Peter Tribble
http://www.petertribble.co.uk/ - http://ptribble.blogspot.com/