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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