zpool vdev vs. glabel

[Ronald Klop]

On Tue, 09 Feb 2010 18:10:21 +0100, Freddie Cash <fjwcash at gmail.com> wrote:

> 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.  :)

Yeah. GEOM is very very very nice. It is a very elegant solution to a lot  
of problems. I always wonder why other OS'es didn't pick it up.

Ronald.


> While ZFS does it's own disk labelling behind the scenes, using glabel  
> just
> makes things easier.