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



Sorry, i did not express myself correct: I do not want to share the logical volumes for the use of a Cluster Filesystem (OCFS etc.). I just want to be able to switch the volume groups from one host to another, so only one host at a time has access to a specific volume group. But if I do an vgimport on a host, every host that sees the VG can use it... I am going to install several Oracle/SAP instances in different Volume Groups and I want to be sure that only one host can access a specific VG at a time. The Veritas Volume Manager for example automatically sets a host id of the system that imports a VG (DiskGroup in Veritas terms) during an import, so any other system has to "force" an import, resulting in a loss of access on the former owner.

Btw: In LVM1 the system ID is used:
..snip..

vgdisplay  VG Name               vg
vgdisplay  System ID             PV_IMPKnoppix1077635774
vgdisplay  Format                lvm1
..snap..

Is this obsolete in LVM2?


Jonathan E Brassow schrieb:
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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read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/



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https://www.redhat.com/mailman/listinfo/linux-lvm
read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/



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