[linux-lvm] "System ID" entry missing in metadata (LVM2) ?!
Andreas Octav
andreas.octav at anykey.de
Wed Oct 18 17:21:55 UTC 2006
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
>>>
>>>
>>> _______________________________________________
>>> linux-lvm mailing list
>>> linux-lvm at redhat.com
>>> https://www.redhat.com/mailman/listinfo/linux-lvm
>>> read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
>>>
>>
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>>
>
>
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