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>A.2. Sharing LVM volumes</H1
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>LVM is not cluster aware</B
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> Be very careful doing this, LVM is not currently cluster-aware
and it is very easy to lose all your data.
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>
If you have a fibre-channel or shared-SCSI environment where more
than one machine has physical access to a set of disks then you can
use LVM to divide these disks up into logical volumes. If you want
to share data you should really be looking at
<A
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>GFS</A
> or other
cluster filesystems.
</P
><P
> The key thing to remember when sharing volumes is that all the LVM
administration must be done on one node only and that all other
nodes must have LVM shut down before changing anything on the admin
node. Then, when the changes have been made, it is necessary to
run vgscan on the other nodes before reloading the volume groups.
Also, unless you are running a cluster-aware filesystem (such as
GFS) or application on the volume, only one node can mount each
filesystem. It is up to you, as system administrator to enforce
this, LVM will not stop you corrupting your data.
</P
><P
> The startup sequence of each node is the same as for a single-node
setup with
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> vgscan
vgchange -ay
</PRE
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>
in the startup scripts.
</P
><P
> If you need to do <STRONG
>any</STRONG
> changes to
the LVM metadata (regardless of whether it affects volumes mounted
on other nodes) you must go through the following sequence. In the
steps below ``admin node'' is any arbitrarily chosen node in the
cluster.
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> Admin node Other nodes
---------- -----------
Close all Logical volumes (umount)
vgchange -an
<make changes, eg lvextend>
vgscan
vgchange -ay
</PRE
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>VGs should be active on the admin node</B
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> You do not need to, nor should you, unload the VGs on
the admin node, so this can be the node with the highest uptime
requirement.
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> I'll say it again: <STRONG
>Be very careful doing
this</STRONG
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