Ok, this could be clear, but in the Cluster_Logical_Volume_Manager.pdf I've read (bottom of page 3): "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, presenting each cluster computer with the same view of the logical volumes"
This is a picture of wath I have in mind: ----------------------------------------- | GFS filesystem | ----------------------------------------- | LV | ----------------------------------------- | VG | ----------------------------------------- | PV1 | PV2 | PV3 | ----------------------------------------- | GNBD1 | GNBD2 | GNBD3 | ----------------------------------------- | hda1 | hda1 | hda1 | | Node1 | Node2 | Node3 | ----------------------------------------- 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. Let's pose this situation: ----------------------------------------------- | GFS | ----------------------------------------------- | LV | ----------------------------------------------- | VG1 | VG2 | ----------------------------------------------- | PV1 | PV2 | | Node1 | Node2 | ----------------------------------------------- | CLVM coordinates | ----------------------------------------------- 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. Is this the correct behaviour?? In the contrary, which is the CLVM role in a cluster? 2008/10/2 Xavier Montagutelli <[EMAIL PROTECTED]> > On Wednesday 01 October 2008 17:39, Angelo Compagnucci wrote: > > Hi to all,This is my first post on this list. Thanks in advance for every > > answer. > > > > I've already read every guide in this matter, this is the list: > > > > Cluster_Administration.pdf > > Cluster_Logical_Volume_Manager.pdf > > Global_Network_Block_Device.pdf > > Cluster_Suite_Overview.pdf > > Global_File_System.pdf > > CLVM.pdf > > RedHatClusterAdminOverview.pdf > > > > The truth is that I've not clear a point about CLVM. > > > > Let's me make an example: > > > > In this example CLVM and the Cluster suite are fully running without > > problems. Let's pose the same configuration of cluster.conf and lvm.conf > > and the nodes of the cluster are joined and operatives. > > Does your example include a shared storage (GNBD, iSCSI, SAN, ...) ? > > > > > NODE1: > > > > pvcreate /dev/hda3 > > > > NODE2: > > > > pvcreate /dev/hda2 > > > > Let's pose that CLVM spans LVM metadata across the cluster, if I stroke > the > > command: > > > > pvscan > > > > I should see /dev/sda2 and /dev/sda3 > > > > and then I can create a vg with > > > > vgcreate /dev/sda2 /dev/sda3 ... > > > > The question is: How LVM metadata sharing works? I have to use GNBD on > the > > row partion to share a device between nodes? I can create a GFS over a > > spanned volume group? Are shareable only logical volumes? > > I have the feeling that something is not clear here. I am not an expert, > but : > > GNBD is just a mean to export a block device on the IP network. A GNBD > device > is accessible to multiple nodes at the same time, and thus you can include > that block device in a CLVM Volume Group. Instead of GNBD, you can also use > any other shared storage (iSCSI, FC, ...). Be careful, from what I have > understood, some SAN storage are not sharable between many hosts (NBD, AoE > for example) ! > > After that, you have the choice : > > - to make one LV with a shared filesystem (GFS). You can then mount the > same > filesystem on many nodes at the same time. > > - to make many LV with an ext3 / xfs / ... filesystem. But you then have > to > make sure that one LV is mounted on only one node at a given time. > > But the type of filesystem is independant, this is a higher component. > > In this picture, CLVM is only a low-level component, avoiding the > concurrent > access of many nodes on the LVM metadata written on the shared storage. > > The data are not "spanned" across the local storage of many nodes (well, I > suppose you *could* do that, but you would need other tools / layers ?) > > Other point : if I remember correctly, the Red Hat doc says it's not > recommended to use GFS on a node that exports a GNBD device. So if you use > GNBD as a shared storage, I suppose it's better to specialize one or more > nodes as GNBD "servers". > > > HTH > > > > > Thanks for your answers!! > > -- > Xavier Montagutelli Tel : +33 (0)5 55 45 77 20 > Service Commun Informatique Fax : +33 (0)5 55 45 75 95 > Universite de Limoges > 123, avenue Albert Thomas > 87060 Limoges cedex > > -- > Linux-cluster mailing list > [email protected] > https://www.redhat.com/mailman/listinfo/linux-cluster >
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