gmirror existing installation?

[Mike Jakubik]

Oliver Fromme wrote:
> Oles Hnatkevych wrote:
>  > There's a simple way of gmirroring existing installation.
>  > 
>  > > sysctl kern.geom.debugflags=16           # allow writing to a live filesystem
>  > > gmirror label -v gm0 /dev/ad0
>  > > # edit /etc/fstab, chane to /dev/mirror/gm0... slices
>  > > # add "geom_mirror_load=YES" to /boot/loader.conf
>  > > # reboot
>  > > gmirror insert gm0 /dev/ad1
>
> I don't recommend to do it that way.  It is better to first
> create the mirror on the second (unused) disk, label and
> newfs it, then copy the system from ad0 to gm0, then boot
> from gm0 on the second disk and insert the first disk into
> the mirror.
>   

Exactly why is this better? It's certainly much more time consuming...