Ocfs2 users - Nov 2007 - OCFS2 + Xen node

Hi all,

I'm trying to use ocfs2 as the root filesystem for xen virtual nodes. If
I leave ocfs2 as a module the system doesn't boot as it doesn't find a
supported filesystem for the root partition. 

I have also tried to include ocfs2 inside the kernel (not as a module)
on the virtual node to be able to mount the root partition but it also
doesnt work. With this option I'm not even able to mount other
partitions as o2cb doesn't find the module.

Has anyone been able to do something similar to this? Do I need to do
anything special to include ocfs2 inside the kernel so I can mount the
root partition at boot?

Jorge Cabello wrote:
> Hi all,
>
> I'm trying to use ocfs2 as the root filesystem for xen virtual nodes.
If
> I leave ocfs2 as a module the system doesn't boot as it doesn't
find a
> supported filesystem for the root partition. 
>
>   
How does the VM access the shared storage? Lets say you use Iscsi.
For the root partition to mount an ocfs2 volume, you will need to log in 
to the iscsi target and then  mount the ocfs2 volume all this handled by 
the initrd. This may be difficult to accomplish. I would start with  
getting a iscsi target (ext3 )  root partition working , then  work on 
ocfs2.
> I have also tried to include ocfs2 inside the kernel (not as a module)
> on the virtual node to be able to mount the root partition but it also
> doesnt work. With this option I'm not even able to mount other
> partitions as o2cb doesn't find the module.
>   
Once again, try mounting the root partition on boot only using iscsi.  
This is easier as you avoid creating a custom initrd.
> Has anyone been able to do something similar to this? Do I need to do
> anything special to include ocfs2 inside the kernel so I can mount the
> root partition at boot?
>
>
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>

Hi,
On Wednesday 07 November 2007 15:21:17 Jorge Cabello
wrote:
> Hi all,
>
> I'm trying to use ocfs2 as the root filesystem for xen virtual nodes.
If
> I leave ocfs2 as a module the system doesn't boot as it doesn't
find a
> supported filesystem for the root partition.
>
> I have also tried to include ocfs2 inside the kernel (not as a module)
> on the virtual node to be able to mount the root partition but it also
> doesnt work. With this option I'm not even able to mount other
> partitions as o2cb doesn't find the module.
When the root filesystem gets mounted by the kernel or inside the initrd all 
prerequisites to mount a that filesystem must be met. In case of cluster 
filesystems like OCFS2 it gets a little bit more complicated compared to 
local filesystems like ext3. That means before mounting you'll have to have
a
cluster running which implicitly means having network up and having started 
ocfs services properly.
This is not done within standard initrd. Even if you hardcompile the module 
into the kernel the network does not get started and there is no cluster 
configuration available in the kernel. All this and if done properly much 
more must be done inside the initrd.
Have a look at 
http://www.opensharedroot.org/documentation/description-on-the-open-sharedroot-bootprocess
>
> Has anyone been able to do something similar to this? Do I need to do
> anything special to include ocfs2 inside the kernel so I can mount the
> root partition at boot?
We've moved the root filesystem successfully onto GFS which is in this way 
comparable to OCFS2 (see www.open-sharedroot.org). The question is not if it 
works for XEN or not but if it works at all (but yes there need to be some 
tweaks for getting XEN up and running I remember. If you like I can sort them 
out again and tell you.).

I've tried to use OCFS2 as root filesystem with that sharedroot concept some
month ago but had problems when using berkely db based software (rpm, 
ldap, ..). That seems to be related to no shared mmaps being available at 
that time. With a more recent kernel that should succeed 2.6.23-.. does have 
the shared mmap support available I've heard.

I hope that helps a bit.

-- 
Gruss / Regards,

Marc Grimme
http://www.atix.de/               http://www.open-sharedroot.org/