Re: [gentoo-user] Duplicate identical Hard Disk

[Mark Knecht]

On Thu, Apr 1, 2010 at 6:40 PM, Joseph <syscon780@×××××.com> wrote:
> On 04/01/10 17:43, Mark Knecht wrote:
>>
>> On Thu, Apr 1, 2010 at 4:02 PM, Paul Hartman
>> <paul.hartman+gentoo@×××××.com> wrote:
>>>
>>> On Thu, Apr 1, 2010 at 5:48 PM, Joseph <syscon780@×××××.com> wrote:
>>>>
>>>> I have two identical HD in the box and want to duplicate sda to sdb;
>>>> sdb is not even partitioned.
>>>> I think I could do:
>>>> dd if=/dev/sda of=/dev/sdb
>>>> but I need to boot from CD isn't it?
>>>
>>> Yes, basically, boot from USB or CD and use ddrescue to clone it, then
>>> edit your fstab and I think you should be good.
>>>
>>> RAID1 would help if a drive physically dies, but if you had any
>>> filesystem corruption or anything you'd just have an identically
>>> corrupt copy on the second disk.
>>
>> A big part of my struggles over the last few days has been with mdadm
>> & RAID1. I'm learning that we don't want to send someone down that
>> path unless he has the right sort of disks. I'm having to deal with
>> returns and reordering due to this.
>>
>> People should be aware of what is really required to do RAID before
>> they get started so they don't duplicate my trials. I wasn't and I'm
>> paying for it. (Almost literally if I don't get the drives in the
>> mail!) ;-)
>>
>> Cheers,
>> Mark
>
> So what you are folks saying is to stay away from RAID-1, beside as Paul
> mention if I get any corruption and/or configuration (due to ebuild) with
> RAID I'll be screwed anyhow.
> So my best option is bootable CD and:
> dd if=/dev/sda of=/dev/sdb
>
> But I'm kind of confused as to how to edit the "sdb" second drive.
> I know I'll have to edit at lest: grub.conf and fstab
> But how?
>
> 1.) Both disk are bootable, (have a boot sector) if I disconnect first one
> sda, I think the second one will be recognize automatically as "sda" isn't
> it?
> 2.) If configure second drive after copying as "sdb" will it still boot if
> fist disk is disconnected?
> --
> Joseph
>
>

With only 2 disks I personally think you're on the right path. With 3
disks I'm personally planning on RAID1 using 3 copies.

If you disconnect the first disk (current sda) then most likely the
original second disk (old sdb) becomes the new first disk. (sda) In
that case no edits are required. However if you make them both
bootable then assuming your BIOS supports it you can tell it to boot
from the second disk. If you want the second disk booting to use the
second disk's copy of Gentoo then you need to edit things to use sdb,
not sda. that's probably overly complicated for what you are trying to
do. I say make the copy, then disconnect the first drive physically
and give it a try.

This all presumes that you comtinue down this path with by hand copies.

My comment about RAID was that I am learning the hard (alas expensive)
way that not all disks can actually do RAID, at least not Linux
software RAID, and really be usable.

Cheers,
Mark