Gmirror - how to do?

[Karl Denninger]

Howdy;

Another quickie someone may know how to handle.

I've got a 2-drive RAID1 mirror I wish to back up.

The easy way appears to be to attach a third drive, let it sync, detach it
and then you have a backup, right?

So I do the following:

	atacontrol attach 2 (attach new disk on external adapter)
	gmirror insert boot ad4s1 (insert the backup into the existing mirror)
	wait (while the disk synchronizes - 3-4 hours)
	gmirror remove boot ad4s1 (remove third copy from mirror)
	atacontrol detach 2 (remove device from the system)

Now I can go pull the carrier "cleanly".

Except for one small problem - when you do this, then try to boot the
backup volume it fails, because gmirror has marked the metadata as "do 
not use" when you removed it, yet the /etc/fstab entries all point to a
mirror that isn't there.

So... how do you accomplish this?

Detach the BUS underlying the drive without warning gmirror first (e.g.
"atacontrol detach 2", without the preceding "gmirror remove"), thereby 
forcing a "dirty" disconnect?  I'd rather not, although if I must, that I 
suppose would work.  However, if I do this, then gmirror thinks I have a
third volume present, and as a consequence as soon I re-init that channel
and geom sees the disk it will immediately begin a rebuild (whether this is
bad or not I suppose is a matter of interpretation)

The bad part of doing it that way that I can identify is that if the machine 
is rebooted it will automatically reattach the 'backup' volume and once that 
starts you're committed to wait for it to finish.  That's not too cool.

Is there a solution to this dilemma that's clean yet leaves me with a
stand-alone bootable backup volume?

--
-- 
Karl Denninger (karl at denninger.net) Internet Consultant & Kids Rights Activist
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