Re: [linux-lvm] "System ID" entry missing in metadata (LVM2) ?!

[Jonathan E Brassow <jbrassow@redhat.com>]

I think it works in the reverse...

vgexport adds a generic tag to the volume groups metadata, basically 
saying "ignore me".  Doing a 'vgs' on an exported volume group shows 
the 'x' attribute; and trying to activate that volume group results in 
"Volume group "<vgname>" is exported".  So, after performing this 
operation, no-one can use the volume group (until vgimport is run).

vgimport removes the generic tag, allowing the VG to be activated and 
used again.  One this command is run, anyone that can see the volume 
group can use/alter the volume group.

Think of it as "import/export from the set of usable volume groups".

If you want to share the VGs, you have two options:
1) Use clustered LVM2.  This is really the best option.
2) Set up your logical volumes on one machine (you should only use 
linear or stripe in this scenario - never mirror or snapshot).  Never 
change the logical volume layout after creating it unless the other 
hosts have deactivated the volume groups being  shared.  Run 'vgchange 
-ay' on all machines that have access to the devices.

Clustered LVM2 makes sure that all changes to a shared volume group are 
serialized to prevent corruption and makes sure to activate/deactivate 
volumes on a cluster-wide basis.   If you are never going to change 
anything (no risk of corruption or inconsistencies), you might be able 
to get away with using LVM2 as it is.

If you need more specialized access, you can use tags.

Note, if you are sharing a logical volume, the application (or file 
system) sharing that volume must be cluster-aware.

  brassow

On Oct 18, 2006, at 11:02 AM, Andreas Octav wrote:

> Hi,
>
> thanks for your response Jonathan, but I want to share the VGs between 
> the hosts. So I hoped that there is something like this functionality:
> -> "vgimport VG" writes some kind of hostid (system_id?) in the 
> metadata
> -> other hosts can�t access the VG
> -> "vgdeport VG" removes the ID, so anyone else can import the VG
>
> My C knowledge isn�t very good, but the sources seem to include a 
> functionality like the one mentioned above.
>
>
> Kind regards,
> Andreas
>
> Jonathan E Brassow schrieb:
>>
>>>> Hi,
>>>>
>>>> i�m new to LVM2 and wondering if it�s possible to restrict access 
>>>> to a
>>>> Volume Group to a single server (e.g. like under vxvm (vxdg
>>>> import/deport)).
>>>> If I import a VG by using vgimport it is still possible to access 
>>>> the
>>>> VG
>>>> on another node in a shared SAN environment. Can I prevent this
>>>> somehow?
>>>>
>>>> I�m using lvm2-2.01.14-3.6 on servers running SuSE SLES9 SP3 x86_64.
>>>>
>>
>> You can use tags to achieve this, or you can specify specific volume 
>> groups and logical volumes in lvm.conf under "volume_list".
>>
>>  brassow
>>
>>
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>>
>
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