Gmirror - how to do?

[Karl Denninger]

On Sun, Feb 06, 2005 at 12:08:42AM +0100, Pawel Jakub Dawidek wrote:
> On Sat, Feb 05, 2005 at 05:04:15PM -0600, Karl Denninger wrote:
> +> > Remember not to boot the main machine with this disk inside, as it can
> +> > be tasted before your main 'boot' mirror. Inserting this disk after
> +> > boot, when your 'boot' mirror is configured should be safe.
> +> 
> +> Nope, won't work.
> +> 
> +> The mirrors potentially have different PHYSICAL slice sizes (remember
> +> this debate a while back on this list?) and if I do this, I'm guaranteed to
> +> screw the partition table, as the fdisk size of the slice table will be
> +> picked up.
> 
> Sorry, but I don't understand.
> How can you touch slices configuration by labeling ad4s1?
> 
> -- 
> Pawel Jakub Dawidek                       http://www.wheel.pl
> pjd at FreeBSD.org                           http://www.FreeBSD.org
> FreeBSD committer                         Am I Evil? Yes, I Am!


Won't the gmirror system create the new mirror (on the "backup disk" using 
the full size of the slice?

If it does, then I can never re-insert that disk into the existing "boot"
mirror.

Here's what I want to be able to do - if its possible.

1. The backup disk needs to remain physically mounted most of the time.
2. Backups are done on a schedule, automatically.
3. The disk is rotated with one in a vault on some schedule to protect
   against catastrophe (e.g. fire, etc)

I can now mount up the partitions separately if necessary to recover a
file or directory if I "oh !@$!" fatfinger something.

This all works ok because the first mirror element was on the smallest
disk, so other elements are 'downsized'.

However, if I do what you're suggesting, the "new" mirror is going to get
created with the size of the slice on the disk involved, which screws me.
I will be able to mount the disks, but I bet if I try to re-integrate the
disk after doing that I get the proverbial "bad address".

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