[CentOS] bare-metal backup before update--options?

[Simon Matter]

> On Mon, Feb 11, 2019 at 04:16:38PM +0100, Simon Matter via CentOS wrote:
>> > Hi all!
>> >
>> > I'm a "nervous nellie", I have not yet updated my 7.5 desktop to 7.6
>> > because (1) it has an Nvidia card, and (2) I've heard of problems
>> > upgrading on top of software RAID (using RAID1 with 2 drives).
>> >
>> > I need to upgrade it to stay secure, and I want to do a bare-metal
>> backup
>> > first (so I can put it all back as it now is, in case it explodes in
>> my
>> > face), so I'm trying to figure out the safest way to do that. Here are
>> > the choices as I see them, I'd appreciate comments/thoughts:
>> >
>> > 1. boot from live DVD and manually reassemble the RAID array (how
>> > would I do that?)
>> > 2. degrade the array (with appropriate commands) so that it is running
>> > on just one drive, then boot a live DVD and use dd to back up that
>> drive.
>> > 3. Other choices you can suggest?
>> >
>> > then after successfully getting a bare-metal backup, reboot it with
>> the
>> > full RAID array and run the update.
>> >
>> > Thanks in advance!
>>
>> To me the easiest method seems to:
>>
>> - boot into rescue mode, not mounting any disks
>> - directly dd all complete disks to files on a USB disk or to a remote
>> host
>> - reboot and update as usual
>>
>> If anything fails you can again boot into rescue mode (maybe with the
>> help
>> of USB/DVD/CD) and:
>>
>> - recover all disks using dd from the backups made before
>> - reboot and be back on 7.5
>>
>> Any reason why this shouldn't work?
>
> Thanks for the reply!
>
> by rescue mode, do you mean (1) the "rescue" kernel in the boot menu?
> Or (2) an option on one of the installer DVDs?
>
> Wouldn't (1) boot from the existing drives and mount them?

I'm not sure about the rescue mode in CentOS 7 but booting from external
media will work for sure.

Simon