I'm setting up a remote server with two identical hard drives, running
FreeBSD-6.1. I want to set the drives up as a mirror for data redundancy. I
also want to be able to break the mirror when I need to update the OS or
installed software, so that if anything goes wrong with the update on one
drive I can boot back to the other one, or if all is well, re-establish the
mirror and synchronise to the updated system. I have serial console access
including BIOS console redirection.

Based on web and Usenet/mailing list searches, gmirror looks more
straightforward for this simple case, gvinum more flexible but poorly
documented, and the most recent comments I can find (still all 6+ months ago)
seem to suggest that gvinum hasn't completely stabilised for production yet.

Is this a fair assessment? Are there any factors I've missed? Which solution
is likely to suit the situation better?


Hello Jonathan,

I run gmirror on all machines which don't have a hardware RAID
controller. I've had drive failures in the past and gmirror handled it
very well. It's now a lot better under 6.1 then 5.x (mostly concerning
the kernel dump area and the swapoff option in rc.conf(5)).

Take a look at Ralf S. Engelschall's documentation on the subject:

Bonus Tip of the day! If you ever have two disk drives which are not
identical, such as these:

ad0: 4112MB <WDC AC24300L 09.09M08> at ata0-master UDMA33
ad3: 4028MB <Maxtor 84320D4 NAVXAA21> at ata1-slave UDMA33

Then make sure you install FreeBSD on the bigger one (i.e. here that
would be ad0) then setup gmirror. If you do the oposite, you will have
a "Consumers too small" error when you try to bring the mirror

Finally, keep in mind that gmirror is only good for RAID 1. If you
need more powerfull volume management tools such as Veritas Volume
Manager or Sun DiskSuite, then you need gvinum.


David Robillard
UNIX systems administrator & Oracle DBA
CISSP, RHCE & Sun Certified Security Administrator
Montreal: +1 514 966 0122
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