[CentOS] Big devices and missing space

[Tim Verhoeven]

On Sat, Mar 29, 2008 at 12:45 PM, Morten Nilsen <morten at runsafe.no> wrote:
> Hello,
>
>  I have a Promise EX 12-port RAID controller in my box, connected to 8
>  750GB disks. I have set up 2 RAID-5 devices and joined these using LVM.
>
>  This is working fine.
>
>  However, there is something that seems wrong..
>  (4-1) * 750 = 2250, but df reports the LVM volume as a mere 4.0T;
>
>  /dev/mapper/storage_volume-stor  4.0T  3.6T  507G  88% /storage
>
>  Shouldn't this be 4.5TB?

No, because storage vendors count in decimal, 750 GB is 750000000000
bytes instead of 805306368000 if you count binary.

So 750 decimal GB is is actually 698 binary GB. And 8 disks in 2 RAID
5 arrays is (6 * 698)/1024 = 4,09 TB (binary).

So it is ok, you did not loose any storage.

Regards,
Tim

-- 
Tim Verhoeven - tim.verhoeven.be at gmail.com - 0479 / 88 11 83

Hoping the problem magically goes away by ignoring it is the
"microsoft approach to programming" and should never be allowed.
(Linus Torvalds)