<div dir="ltr">Ok, this could be clear, but in the <span class="Apple-style-span" style="border-collapse: collapse; ">Cluster_Logical_Volume_Manager.pdf</span> I've read (bottom of page 3):<div><br></div><div><span style="border-collapse:collapse"><span style="font-size:small">"The clmvd daemon is the key clustering extension to LVM. The clvmd daemon runs in each cluster computer and distributes LVM metadata updates in a cluster, </span><span style="text-decoration:underline"><span style="font-size:small">presenting each cluster computer with the same view of the logical volumes"</span></span></span></div>
<div><span style="border-collapse:collapse;text-decoration:underline"><br></span></div><div><span style="border-collapse:collapse">This is a picture of wath I have in mind:</span></div>
<div><span style="border-collapse:collapse"><br></span></div><div><span style="border-collapse:collapse">-----------------------------------------</span></div><div><span style="border-collapse:collapse">| GFS filesystem |</span></div>
<div><span style="border-collapse:collapse">-----------------------------------------</span></div><div><span style="border-collapse:collapse">| LV |</span></div>
<div><span style="border-collapse:collapse">-----------------------------------------</span></div><div><span style="border-collapse:collapse">| VG |</span></div>
<div><span style="border-collapse:collapse">-----------------------------------------</span></div><div><span style="border-collapse:collapse">| PV1 | PV2 | PV3 |</span></div>
<div><span style="border-collapse:collapse">-----------------------------------------</span></div><div><span style="border-collapse:collapse">| GNBD1 | GNBD2 | GNBD3 |</span></div>
<div><span style="border-collapse:collapse">-----------------------------------------</span></div><div><span style="border-collapse:collapse">| hda1 | hda1 | hda1 |</span></div>
<div><span style="border-collapse:collapse">| Node1 | Node2 | Node3 |</span></div><div><span style="border-collapse:collapse">-----------------------------------------</span></div>
<div><span style="border-collapse:collapse"><br></span></div><div><span style="border-collapse:collapse">In this case the clvm features are not useful because there is only one machine (that could not be a node of a cluster) that have the lvm over GNBD exported devices. So the nodes doesn't know nothing about the other nodes.</span></div>
<div><span style="border-collapse:collapse"><br></span></div><div><span style="border-collapse:collapse">Let's pose this situation:</span></div><div><span style="border-collapse:collapse"><br>
</span></div><div><span style="border-collapse:collapse">-----------------------------------------------</span></div><div><span style="border-collapse:collapse">| GFS |</span></div>
<div><span style="border-collapse:collapse">-----------------------------------------------</span></div><div><span style="border-collapse:collapse">| LV |</span></div>
<div><span style="border-collapse:collapse">-----------------------------------------------</span></div><div><span style="border-collapse:collapse">| VG1 | VG2 |</span></div>
<div><span style="border-collapse:collapse">-----------------------------------------------</span></div><div><span style="border-collapse:collapse">| PV1 | PV2 |</span></div>
<div><span style="border-collapse:collapse">| Node1 | Node2 |</span></div><div><span style="border-collapse:collapse">-----------------------------------------------</span></div>
<div><span style="border-collapse:collapse">| CLVM coordinates |</span></div><div><span style="border-collapse:collapse">-----------------------------------------------</span></div>
<div><span style="border-collapse:collapse"><br></span></div><div><span style="border-collapse:collapse">In this situatuation makes sense to have a clustered lvm because if I have to make some maintenance over VGs, CLVM can lock and unlock the interested device.</span></div>
<div><span style="border-collapse:collapse"><br></span></div><div><span style="border-collapse:collapse">Is this the correct behaviour??</span></div><div><span style="border-collapse:collapse"><br>
</span></div><div><span style="border-collapse:collapse">In the contrary, which is the CLVM role in a cluster?</span></div><div><span style="border-collapse:collapse"> <br>
</span><br><div class="gmail_quote">2008/10/2 Xavier Montagutelli <span dir="ltr"><<a href="mailto:xavier.montagutelli@unilim.fr" target="_blank">xavier.montagutelli@unilim.fr</a>></span><br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>On Wednesday 01 October 2008 17:39, Angelo Compagnucci wrote:<br>
> Hi to all,This is my first post on this list. Thanks in advance for every<br>
> answer.<br>
><br>
> I've already read every guide in this matter, this is the list:<br>
><br>
> Cluster_Administration.pdf<br>
> Cluster_Logical_Volume_Manager.pdf<br>
> Global_Network_Block_Device.pdf<br>
> Cluster_Suite_Overview.pdf<br>
> Global_File_System.pdf<br>
> CLVM.pdf<br>
> RedHatClusterAdminOverview.pdf<br>
><br>
> The truth is that I've not clear a point about CLVM.<br>
><br>
> Let's me make an example:<br>
><br>
> In this example CLVM and the Cluster suite are fully running without<br>
> problems. Let's pose the same configuration of cluster.conf and lvm.conf<br>
> and the nodes of the cluster are joined and operatives.<br>
<br>
</div>Does your example include a shared storage (GNBD, iSCSI, SAN, ...) ?<br>
<div><br>
><br>
> NODE1:<br>
><br>
> pvcreate /dev/hda3<br>
><br>
> NODE2:<br>
><br>
> pvcreate /dev/hda2<br>
><br>
> Let's pose that CLVM spans LVM metadata across the cluster, if I stroke the<br>
> command:<br>
><br>
> pvscan<br>
><br>
> I should see /dev/sda2 and /dev/sda3<br>
><br>
> and then I can create a vg with<br>
><br>
> vgcreate /dev/sda2 /dev/sda3 ...<br>
><br>
> The question is: How LVM metadata sharing works? I have to use GNBD on the<br>
> row partion to share a device between nodes? I can create a GFS over a<br>
> spanned volume group? Are shareable only logical volumes?<br>
<br>
</div>I have the feeling that something is not clear here. I am not an expert, but :<br>
<br>
GNBD is just a mean to export a block device on the IP network. A GNBD device<br>
is accessible to multiple nodes at the same time, and thus you can include<br>
that block device in a CLVM Volume Group. Instead of GNBD, you can also use<br>
any other shared storage (iSCSI, FC, ...). Be careful, from what I have<br>
understood, some SAN storage are not sharable between many hosts (NBD, AoE<br>
for example) !<br>
<br>
After that, you have the choice :<br>
<br>
- to make one LV with a shared filesystem (GFS). You can then mount the same<br>
filesystem on many nodes at the same time.<br>
<br>
- to make many LV with an ext3 / xfs / ... filesystem. But you then have to<br>
make sure that one LV is mounted on only one node at a given time.<br>
<br>
But the type of filesystem is independant, this is a higher component.<br>
<br>
In this picture, CLVM is only a low-level component, avoiding the concurrent<br>
access of many nodes on the LVM metadata written on the shared storage.<br>
<br>
The data are not "spanned" across the local storage of many nodes (well, I<br>
suppose you *could* do that, but you would need other tools / layers ?)<br>
<br>
Other point : if I remember correctly, the Red Hat doc says it's not<br>
recommended to use GFS on a node that exports a GNBD device. So if you use<br>
GNBD as a shared storage, I suppose it's better to specialize one or more<br>
nodes as GNBD "servers".<br>
<br>
<br>
HTH<br>
<br>
><br>
> Thanks for your answers!!<br>
<font color="#888888"><br>
--<br>
Xavier Montagutelli Tel : +33 (0)5 55 45 77 20<br>
Service Commun Informatique Fax : +33 (0)5 55 45 75 95<br>
Universite de Limoges<br>
123, avenue Albert Thomas<br>
87060 Limoges cedex<br>
</font><div><div></div><div><br>
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</div></div></blockquote></div><br></div></div>