zpool vdev vs. glabel

Freddie Cash fjwcash at gmail.com
Tue Feb 9 17:10:23 UTC 2010

On Tue, Feb 9, 2010 at 6:26 AM, Jeremy Chadwick <freebsd at jdc.parodius.com>wrote:

> Also, I'm a little confused as to the use of glabel in this case.  In
> what condition do your disk indices (e.g. X of daX) change?  Are you
> yanking multiple disks out of a system at the same time and then shoving
> them back into different drive bays?  Are you switching between storage
> subsystem drivers (ahci(4) vs. ataahci(4), for example) regularly?
> I've yet to be convinced glabel is worth bothering with, unless the
> system adheres to one of the above situations (which are worthy of
> strangulation anyway ;-) ).
> Use multiple disk controllers in a server, and watch as kernel updates
and/or BIOS updates change the order that the controllers are probed, thus
changing the dev node for every disk in the system.

Use multiple disk controllers that use CAM, then move from an IDE-based
CompactFlash adapter to a SATA-based CompactFlash adapter for the /
filesystem, and watch the system renumber all your dev nodes.

Use a RAID controller configured for JBOD or "Single Disk" arrays, and
replace a drive while the server is running, which assigns the disk "largest
da number +1", then renumbers everything when the server reboots.

After you run into those kinds of things a few times, you'll start to use
glabel(8) for everything.  Plus, it just makes things easier to understand.
 Instead of da0 through da25 which is a mix of SATA, RAID, and USB drives,
you have cfdisk0, cfdisk1, disk00 through disk24, and so on.

Personally, the greatest thing to ever happen to FreeBSD is the introduction
of GEOM, and the addition of the glabel class.  :)

While ZFS does it's own disk labelling behind the scenes, using glabel just
makes things easier.
Freddie Cash
fjwcash at gmail.com

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