question regarding geom labels

[Alexander Best]

On Fri Mar 30 12, Warren Block wrote:
> On Fri, 30 Mar 2012, Alexander Best wrote:
> 
> >i have a question regarding a label for a swap partition. when should i do 
> >the
> >labeling? after or before creating the partition scheme?
> >
> >when i label before creating the partition scheme, likes this:
> >
> >glabel label -v swap /dev/da0
> >gpart create -s GPT /dev/da0
> >
> >i get the following warning:
> >
> >GEOM: da1: the secondary GPT header is not in the last LBA.
> >
> >which is obvious, because the label is being written into the last LBA and 
> >thus
> >the backup GPT header gets written into the last-1 LBA.
> 
> Right.  Don't do that, the GPT backup header needs to be at the end of 
> the physical device.  If you're using that whole disk for swap, there's 
> no need for a partition anyway.
> 
> >if i create the partitioning scheme before labeling the device, like this:
> >
> >gpart create -s GPT /dev/da0
> >glabel label -v swap /dev/da0
> >
> >or
> >
> >gpart create -s GPT /dev/da0
> >gpart add -t freebsd-swap /dev/da0
> >glabel label -v swap /dev/da0p1
> >
> >the label gets written into da0 or da0p1 and is at constant risk of being
> >overwritten by userdata.
> 
> No.  The swap device entered in /etc/fstab would be /dev/label/swap, 
> which is one block smaller than da0p1.  That's the last-block metadata, 
> it's safe.

thanks for the info. :)

> 
> But if the whole disk is for swap, skip the partitioning entirely.