Using mirroring to replace drive?

[Chris Pratt]

Hi, For years I've been upgrading by building a temp
server, transferring a production function to it and
temporarily decommissioning the one server while
I upgrade and rebuild it. I was thinking of trying a different
approach since having tried out gvinum in the last
couple of years.

The current scenario is that I have a machine where the
adaptec controller is suggesting I replace a failing SCSI
drive which happens to be the system disk. I purchased
a couple of new drives and thought I might just plug it in
and mirror the failing drive on the new drive. Then
pull the failing drive and plug in the other new drive as
the second mirrored drive and be done with it. One
obvious outcome would be a having a system drive
mirror for future such issues. I have never built a mirror
on the fly but it seems many have from what I've read
and the cookbooks out there make it sound very
easy. I was going to use GEOM Mirror on 6.2 (then
upgrade to 7.0 after establishing the new good drives).

1. Is this an appropriate way to deal with this?

2. Are there any high risk aspects of doing this while running
a server in production? I'm thinking of things like how
probable it is of trashing the original disk, making the
system unbootable in the process etc?

3. Are there better approaches that are safer (aside from
my normal hardware swap MO).

4. Does using GEOM Mirror RAID-1 make the upgrade from
6.2 to 7.0 a dangerous proposition. I do upgrades via
cvsup and buildworld.

The environment is
	FreeBSD 6.2
	Supermicro with Adaptec SCSI
	All ~73 GB Maxtor and Seagate drives
		Current da0 system is Maxtor, there
		will be minor size differences, the
		replacement Cheetah is a hair larger.
	Apache, PHP5 and Mysql
	No existing RAID Configuration