Centos 6 upgrade to 7

I am running a remote centos 6.6, need to upgrade to 7 and feel there are too many chances that something could go wrong if I upgrade. Therefore, I am thinking about installing a second drive, then mounting an ISO so I can install centos 7 onto the new drive. However, before making it live, I need to be able to copy everything needed from sad1 first.

This is where things get unknown for me since I've not done a remote upgrade like this before.

I want to make sure I have installed everything I need into the new os, then I need to boot off the new drive, to make sure it is working as it should. If so, then I need to remove the old drive and leave the new one installed.

Since there will be two physical drives, I'm not sure how to deal with the drive designations.
For example, when I start, I'll have my first drive as sda1 and my second new drive as sdb1.

When I install, I'll want to install a boot loader onto sdb1 but at some point, that drive will become the only drive.
When the first drive is pulled out, will the second drive automatically become sda1 again and boot as it always has?
projectsAsked:
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andreasSystem AdminCommented:
1st. You are correct with installing new. Its the recommended way. The sister distribution Scientific Linux does not even support major upgrades.

2nd best would be you try to do it before you do it on the remote machine. Ive not done it myself bout your point with the bootloader is a good point.

But why you just dont fix it after you have pulled the drive. (or doesnt you have a remote console access (at bios level) and you need a booting OS to access the server)?

If you only can access a booted OS there are many things could go wrong not just bootloader.

e.g. missing ssh keys, changes host keys. Bugs regarding the network connection so that after 1st boot the OS doesnt have network. etc. pp.

Does Centos even support an installation to an additional disk started on a running system and not via boting from the installation CD/DVD?
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projectsAuthor Commented:
I have remote kvm access so I'm ok there.

Not sure what the following means?

>But why you just dont fix it after you have pulled the drive. (or doesnt you have a remote console
>access (at bios level) and you need a booting OS to access the server)?
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andreasSystem AdminCommented:
I mean dont worry about the correct boot loader installation in the 1st place. If its wrong after the physical disk is pulled and it doesnt boot then you just boot a rescue environment and fix the bootloader.
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projectsAuthor Commented:
I installed the minimal version last night and cannot believe how changed centos is. I had so many problems I decided I better install the DVD version instead of minimal to get some extra help.

Have to install that and take a look at it before I even consider trying this.

Can you think of any other issues with adding a drive, installing onto that, then removing it? Like maybe having the second disk installed, doing the install from CLI so I don't have to take the server down, then copying what ever I need over then doing a test boot off the new drive?
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andreasSystem AdminCommented:
im not sure if centos can do a CLI interface from within a running linux. Need to check this out myself first when i have a chance to do so. Maybe others may have insight in that point.

Else install inside a vm (lvm based setup) then change hdd priority in server and mirror back the vm to physical host and then adjust drivers.

If downtime is important for you try this first on a test system. Hardware might be different its just to be confident with the procedure.
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projectsAuthor Commented:
Great idea! I had already installed a vm using C7 but had not thought about adding a drive and going through the whole process.

Perfect solution, thanks.
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