Re: [Xen-users] bsd disklabel & lvm

[Nico Kadel-Garcia <nkadel@xxxxxxxxx>]

Dylan Martin wrote:
> > > Okay, here's another question that no one will be able to answer.
> > >
> > > I have an OpenBSD HVM domU, and I wanted to mount its filesystem in
> > > my Linux dom0.  The domU's disk lives on a logical volume.  Kpartx
> > > does detect that partition 4 contains the disklabel, but that's as far
> > > as I get.
> > >
> > > I think my fedora kernel just doesn't support disklabels...
> > >
> > > Anyone know how this is supposed to work?
> > >  
> > >       
> > So why use them. Disklabels for ext2 and ext3 are useful abut the 
> > partitions can still be accessed as /dev/hda1, /dev/VolGroup00/whatever, 
> > or if you use "kpartx -a /dev/VolGroup00/whatever" then you can access 
> > /dev/mapper/whatever0, /dev/mapper/whatever1, etc.
> > Or did you do something too clever and use LVM instide of the OpenBSD 
> > DomU and need to go through extra arcanery?
> >     
> I think there is some file system label and disklabel confusion here.
> Disklabel is like fdisk for bsd.. sort of.  In PC hardware when
> running bsd, you first have to partition your disk using fdisk.  If
> you're only running one OS, you just make one partition with all the
> space in it.  Then you take that partition and break it up into
> sub-partitions (for lack of a better word) using disklabel.  I think
> the reason for this has to do with PC hardware vs. other kinds that
> don't use dos-type partition tables.  
>   
Ahhh. Extended partitions! OK, that becomes more comprehensible.

There's frankly no reason to do it for Xen guest domains: Simply add the 
new host partitions as new drives, /dev/sda or /dev/xvda dep, and break 
them down into up to 4 individual sub partitions per the maximum 
classical "primary" partitions, unless you're in love with the old 
multi-multi-partition model of /, /usr, /tmp, /var/tmp, /var, 
/var/spool, /usr/local, /lenny, /joey, 
/usr/var/beta/gamma/mygreat/ant/matilda/, etc.
There were reasons to do that much partitoning 20 years ago when drives 
were much smaller and more expensive and gnu-tar didn't exist yet and we 
did UNIX backups with "dump".: they're mostly gone now..
> Anyway, the upshot is that in order for Linux to see my OpenBSD
> partitions, it would have to read the disklabel to know where my
> filesystems are.
>
> Another way to say it is:
>
> [dom0          ...]
> [lv           ] 
> [fdisk part   ]
> [disklabel    ]
> [wd0a][wd0d]..
>
> -Dylan
>   
It really sounds like an extended partition table residing on LVM 
partition. I'm sure there are tools to pull that out of a Linux Xen 
partition, I just don't know what they are off the top of my head.
_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users