Re: [gentoo-user] Duplicate identical Hard Disk

[Joseph <syscon780@gmail.com>]

On 04/02/10 07:59, Mark Knecht wrote:
>Good questions:
>
>1) Yes, you can RAID partitions of drives. That's what I'm doing. You
>can look at the Gentoo RAID/LVM Install guide to see an example of
>using RAID0 and RAID1 on a single drive.
>
>http://www.gentoo.org/doc/en/gentoo-x86+raid+lvm2-quickinstall.xml
>
>2) I'm certainly not suggesting RAID doesn't work. It's just not
>working for me, either due to new motherboard hardware or due to the
>drives themselves. I'm currently betting it's the drives. The
>background info, without getting too deeply into it, is that if the
>drive supports SMART and SMART is enabled, then when doing RAID you
>need guaranteed Time Limited Error Recovery (TLER) to ensure (I think)
>that SMART works doesn't get in the way of the drive responding in the
>appropriate amount of time or else the drive will fall out of the RAID
>array. Turns out the WD  (according to different mailing list and
>forums I've been looking at) has removed TLER on almost all of their
>Green drive and some/many/most of the Blue and Black series. They are
>supporting this in the RE drives though of which I've obtained two.
>They are smaller and more expensive, but built for RAID, so I'm going
>to try them out next.
>
>http://en.wikipedia.org/wiki/Time-Limited_Error_Recovery
>
>3) As I understand the subject you are correct about size and speed,
>but a 3-disk RAID5 array can stand 1 disk failing whereas a 3-disk
>RAID1 array can stand 2 disks failing. For this app (MythTV and seldom
>used backup server) I don't need speed and size isn't a huge issue so
>I chose 3-disk RAID1. (Note that the HTPC case I'm using supports up
>to 3 drives only.) Because multiple drives purchased at the same time
>generally come from the same production lot there's an additional
>danger that if one drive fails then one more (or all) could fail at
>the same time so I'm protecting myself against that. Again, this is
>very specific to my current needs which is really to back up another
>machine which will be RAID0 as it needs more disk I/O speed to support
>12 processor cores.
>
>As always, I'm certainly interested in info and ideas on this subject,
>most especially now when I'm buying and building.
>
>Cheers,
>Mark

I'm not even sure if any RAID is a solution for me.
My situation is a follow, I've configured Gentoo box for a medical clinic and I'll administer it reportedly via ssh.
One server running Windows XP in VirtualBox and some other Linux programs. 
Server is a quad core ADM and has two identical SATA drives about 600GB
There is another smaller box (Intel ATOM CPU) running Gentoo, this box runs Asterisk and VirtualBox as well, it is a server backup. If something happens to 
mains Server, user just presses "Scroll Lock" twice (KVM), logs in into smaller and runs the main program from there.  So I have a backup in place.

I just want to utilize the second drive of the main server.  I'm mostly concerns about the problems with emerge, not the hard drive failure (I've plenty of 
backups).
So, I think the best option for me is to just mirror the first HD and modify it to use it a sdb. I'm just making steps I need to do:

1.) Boot from external CD
dd if=/dev/sda of=/dev/sdb

2.)
modify (add to) grub.conf on sda
#title boot sda current
title=1st HD sda Kernel Current
root (hd0,0)
kernel /boot/kernel-current root=/dev/sda3

#title boot sdb current
title=2nd HD sdb Kernel Current
root (hd1,0)
kernel /boot/kernel-current root=/dev/sdb3

3.) Modify fstab

Walt has mentioned to use "rdev" but reading man pages it is only i386, and all my boxes running amd64 (x86_64).

What else did I miss. 

-- 
Joseph