CentOS - Sep 2014 - Advice on CentOS 7, software raid 1, lvm, 3 TB disks

Greetings -

I am preparing to order a new desktop system for work.  In general the new 
system will be a Dell Precision T3610 with two 3 TB drives.  I plan on 
installing CentOS 7 as a KVM host, with virtual machines for Win 7 Pro and 
Linux Mint.  I am looking for some advice or a good how-to on configuring 
software raid on the two drives, then using LVM for the host and virtual 
machines.  I have configured our company server (Dell T610) with hardware 
raid and LVM for a CentOS 6 KVM host and several virtual machines so I am 
not a complete novice, but have never setup a Linux software raid system, 
and have not played with a CentOS 7 install yet.  I have been searching the 
web and forums for information and am not finding much for good guidance. 
Lots of gotcha's are popping up identifying issues related to CentOS 7, 
software raid 1, grub install, > 2 TB disks (or any combination of these 
factors).  The CentOS Wiki has a good description of installing CentOS 5 
with raid 1, but there is a big warning about being an unsupported (risky) 
approach.  Can anyone point me to a good how-to, or provide some general 
guidance.  Thanks.

Jeff Boyce
www.meridianenv.com

On Tue, Sep 16, 2014 at 6:07 PM, Jeff Boyce <jboyce at meridianenv.com>
wrote:
> Greetings -
>
> I am preparing to order a new desktop system for work.  In general the new
> system will be a Dell Precision T3610 with two 3 TB drives.  I plan on
> installing CentOS 7 as a KVM host, with virtual machines for Win 7 Pro and
> Linux Mint.  I am looking for some advice or a good how-to on configuring
> software raid on the two drives, then using LVM for the host and virtual
> machines.  I have configured our company server (Dell T610) with hardware
> raid and LVM for a CentOS 6 KVM host and several virtual machines so I am
> not a complete novice, but have never setup a Linux software raid system,
> and have not played with a CentOS 7 install yet.  I have been searching the
> web and forums for information and am not finding much for good guidance.
> Lots of gotcha's are popping up identifying issues related to CentOS 7,
> software raid 1, grub install, > 2 TB disks (or any combination of these
> factors).  The CentOS Wiki has a good description of installing

I'm not sure which wiki article you might have read.  That URL might be
worthwhile to share.

> CentOS 5 with raid 1, but there is a big warning about being an
> unsupported (risky) approach.  Can anyone point me to a good how-to, or
> provide some general guidance.  Thanks.
>
>
Hopefully what I have typed up below helps you.
I don't know about soft-raid1 being an unsupported/risky approach ... that
said I'd pick hardware raid over software raid (considering I had spare
hardware) so I don't have to fuss with raid at the OS level.  I have worked
on a mix of software-raid and hardware-raid systems (and still do) ... each
has its own pros/cons.  I've had success re-adding a new drive in degraded
soft-raid1 arrays in a production environment ... so I say go for it.

[ ]
Somebody else asked about C7 and soft-raid in the past week or week and a
half.
You can find that thread here:
http://lists.centos.org/pipermail/centos/2014-September/145656.html
Though I don't think much was accomplished in that thread.
[/]


My suggestion to you (as well as that last person) is to spin up a VM (or
spare bare-metal hardware) and use mdadm commands to assemble, stop,
hot-fail, hot-remove, and rebuild (add a new disk to replace a "failed
one") your soft-raid array.

As is the case with many things Linux, the manpage is your friend.
 Sometimes sysadmins and hobbyists decide to publish what they've done
(good or bad) which can be found with the search engine of your choice.

In this case, even generic (non-RH or non-CentOS specific) command
documentation is likely what you want.  More than likely you'll get the
results you want by booting to a rescue CD (or switching to a shell on your
install CD), setting up your soft-raid, then booting to your install CD,
which will probe for your disk/soft-raid/lvm layout.

steps for graphical approach (C5, so dated) -
http://wiki.centos.org/HowTos/SoftwareRAIDonCentOS5
partitionable soft-raid -
http://wiki.centos.org/HowTos/Install_On_Partitionable_RAID1
TLDP create soft-raid - http://www.tldp.org/HOWTO/Software-RAID-HOWTO.html
Arch Linux create soft-raid -
https://wiki.archlinux.org/index.php/Software_RAID_and_LVM
repairing - http://www.thomas-krenn.com/en/wiki/Mdadm_recovery_and_resync
repairing - http://ethertubes.com/repair-md-mdadm-raid/
repairing -
http://blog.laimbock.com/2014/04/01/how-to-replace-a-failed-disk-with-linux-software-raid-mdadm/

-- 
---~~.~~---
Mike
//  SilverTip257  //