[CentOS] Software RAID in CentOS (EL)

[Michael Boman]

On 4/19/05, Chuck Rock <carock at epctech.com> wrote:
> Is it just me, or does anyone see something seriously wrong with the
> Software RAID example?
> 
> http://mirrors.cat.pdx.edu/centos/3/docs/html/rhel-sag-en-3/ch-software-raid
> .html
> 
> Figure 12-4
> 
> Isn't RAID supposed to be redundant disks, not redundant partitions? If that
> hda disk goes bad, the raid and redundancy is nowhere to be found along with
> your data. Right?

Correct. My guess is that the person who did the screenshots didn't
have two drives, or something like that.

> Is there a way to make each disk a single software raid partition, then use
> slices of that partition for your drive partitions with LVM or something? I
> basically want to encapsulate the partitions for the operating system with
> RAID so that if a disk drive fails, it can be repaired.

LVM is pretty cool when you want to concat or split drives out. So for
an example you create a single big raid on the drives, and then use
LVM to "partition" it (create logical volumes) for the various
mountpoints. LVM is also pretty cool when it comes to expanding your
storage; let's say that you start out with RAID1 on two disks, and
then at a later stage buy two more disks (which you also do RAID1 on)
you can use LVM to grow the "partitions" (volumes).

> I have never used this function before, so set me straight if I'm just
> missing the point.

LVM doesn't do RAID (well, you can do striping [RAID0]), and you
should combine [hardware/software] raid with LVM. And needless to say,
RAID is not a substitute for backups.

Best regards
 Michael Boman