AW: RAID greater than 2TB on Fedora Core 3

[Masopust Christian]

hi scot,

it's a RAID5 with 8 x 400GB disks, so i'd expected a size of
appr. 2,8TB (Raid says it's about 2,6TB) but Fedora only see
exactly 2TB....

thanks,
Christian


-----Ursprüngliche Nachricht-----
Von: fedora-list-bounces at redhat.com [mailto:fedora-list-bounces at redhat.com]
Im Auftrag von Scot L. Harris
Gesendet: Montag, 04. April 2005 17:14
An: 'fedora-list at redhat.com'
Betreff: Re: RAID greater than 2TB on Fedora Core 3

On Mon, 2005-04-04 at 10:45, Masopust Christian wrote:
> Dear all,
> 
> maybe this is a dumb question from an newbie, but...  ;-)
> 
> I've connected a RAID with appr. 2,6TB to my new installed
> Fedora-System (Fedora Core 3, Adaptec 39160 and RAID is an
> EonStore).
> 
> When running fdisk the biggest partition i can create is 2TB!
> 
> when trying to create the filesystem with mkfs.xfs directly
> on /dev/sda i also get only 2TB !
> 
> so, what am i doing wrong?   is the adaptec 39160 the problem?
> (this because i read something about such big raids working
> with 3ware 9000 RAID cards)

What raid level are you trying to setup?

Each raid level utilizes the available drives in different ways which
result in the usable space being different.  If you have 2.6 TB of raw
disk space and use Raid 1 (simple mirroring) you would only be able to
create a file system with a size of 1.3 TB.  

The different raid levels provide some trade offs in usable space vs.
speed of writes vs. speed of reads vs. resiliency.

Raid 5 will have a 20% overhead  due to the way it replicates data
across multiple drives.  

If you are just trying to use all of the raw disk space you have in a
single file system then you probably don't want raid, you want to use
LVM.  LVM creates logical volumes across multiple drives and allows you
to create very large file systems.  Understand though that this is not
raid, it does not provide redundancy if one of the hard drives fails.

  
-- 
Scot L. Harris
webid at cfl.rr.com

Mollison's Bureaucracy Hypothesis:
	If an idea can survive a bureaucratic review and be implemented
	it wasn't worth doing. 

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