[nflug] RAID

Rob Dege livemotion at gmail.com
Fri Feb 8 14:36:23 EST 2008


It's been a while since I've spoken in RAID, but I think your terminology is
off.  RAID-0 by default requires at least two hard drives in order to
configure.  The same goes for RAID 1.

So, in this instance, you will use two drives to create a RAID-0 array.
This array now appears as a single drive.  You then create another RAID-0
array using the other two disks.  This array now appears as a single drive.
So now, you have two RAID0 arrays independent of each other.  Finally, you
create a RAID-1 mirroring array, using the two RAID-0 disks that you just
created.

Thus, you now have a single drive, with the capacity of two drives.  If this
is all handled within the RAID controller, linux will only acknowledge the
existence of this RAID-0+1 drive as a single disk.  So you won't be able to
use the linux software RAID to create another layer of mirroring.

Of course, this is assuming that your RAID controller is doing all of the
array structure and work.  Most of the onboard RAID controllers in today's
motherboards, and built shoddy.  Their contain the cheap hardware, but you
need to install software to configure/access the onboard controller.

Plus, it's been a while, but I do recall some warning about not putting
either the root directory or the /boot directory on a raid.  It has
something to do about the module needed by the kernel to identify the raid
drive being stored on the raid drive or something like that.

oh well, hope this helps somewhat.

-Rob


On Feb 8, 2008 12:49 PM, Eric #4011 <eric at bootz.us> wrote:

> Hi, I was wondering if the following RAID configuration is possible?
>
>
> I have 4 SATA drives for RAID and am using MediaShield utility to
> configure a RAID 0+1
>
> ***********************************************************************************************
> MediaShield States RAID 0+1 is:
>         RAID 0 drives can be mirrored using RAID 1 techniques,
> resulting in a RAID 0+1 solution
>         for improved performance plus resiliency
>         The controller combines the performance of data striping (RAID
> 0) and the fault tolerance
>         of disk mirroring (RAID 1). Data is striped across multiple
> drives and duplicated on
>         another set of drives.
>
> ***********************************************************************************************
>
>
> After this I have two drives and I am ready to install linux(debian etch)
>
> My thoughts are if I also use RAID 1 software(linux) with the existing
> two drives I will have one hard drive writing to three hard drives?
>
> I'm wondering if this is possible?
>
> Thank you in advance for your explanations
>
> Thank you,
> Eric
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-- 
-Rob

Ben Franklin Quote: "They that can give up essential liberty to obtain a
little temporary safety deserve neither liberty nor safety."
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