5.5. Creating a Mirrored LVM Logical Volume in a Cluster Creating a mirrored LVM logical volume in a cluster requires the same commands and procedures as creating a mirrored LVM logical volume on a single node. However, in order to create a mirrored LVM volume in a cluster the cluster and cluster mirror infrastructure must be running, the cluster must be quorate, and the locking type in the lvm.conf file must be set correctly to enable cluster locking, either directly or by means of the lvmconf command as described in Section 3.1, "Creating LVM Volumes in a Cluster" . The following procedure creates a mirrored LVM volume in a cluster. First the procedure checks to see whether the cluster services are installed and running, then the procedure creates the mirrored volume. In order to create a mirrored logical volume that is shared by all of the nodes in a cluster, the locking type must be set correctly in the lvm.conf file in every node of the cluster. By default, the locking type is set to local. To change this, execute the following command in each node of the cluster to enable clustered locking: To create a clustered logical volume, the cluster infrastructure must be up and running on every node in the cluster. The following example verifies that the clvmd daemon is running on the node from which it was issued: The following command shows the local view of the cluster status: Ensure that the cmirror and cmirror-kernel packages are installed. The cmirror-kernel package that must be installed depends on the kernel that is running. For example, if the running kernel is kernel-largesmp , it is necessary to have cmirror-kernel-largesmp for the corresponding kernel version. Start the cmirror service. Create the mirror. The first step is creating the physical volumes. The following commands create three physical volumes. Two of the physical volumes will be used for the legs of the mirror, and the third physical volume will contain the mirror log. Create the volume group. This example creates a volume group mirrorvg that consists of the three physical volumes that were created in the step. Note that the output of the vgcreate command indicates that the volume group is clustered. You can verify that a volume group is clustered with the vgs command, which will show the volume group's attributes. If a volume group is clustered, it will show a c attribute. Create the mirrored logical volume. This example creates the logical volume mirrorlv from the volume group mirrorvg . This volume has one mirror leg. This example specifies which extents of the physical volume will be used for the logical volume. You can use the lvs command to display the progress of the mirror creation. The following example shows that the mirror is 47% synced, then 91% synced, then 100% synced when the mirror is complete. The completion of the mirror is noted in the system log: You can use the lvs with the -o +devices options to display the configuration of the mirror, including which devices make up the mirror legs. You can see that the logical volume in this example is composed of two linear images and one log. For release RHEL 4.8 and later, you can use the seg_pe_ranges option of the lvs to display the data layout. You can use this option to verify that your layout is properly redundant. The output of this command dispays PE ranges in the same format that the lvcreate and lvresize commands take as input. When you create the mirrored volume, you create the clustered_log dlm space, which will contain the dlm logs for all mirrors. Note For information on recovering from the failure of one of the legs of an LVM mirrored volume, see Section 6.3, "Recovering from LVM Mirror Failure" .

Commands:
/usr/sbin/lvmconf --enable-cluster
ps auxw | grep clvmd root 17642 0.0 0.1 32164 1072 ? Ssl Apr06 0:00 clvmd -T20 -t 90
cman_tool services Service Name GID LID State Code DLM Lock Space: "clvmd" 7 3 run - [1 2 3]
service cmirror start Loading clustered mirror log: [ OK ]
pvcreate /dev/xvdb1 Physical volume "/dev/xvdb1" successfully created pvcreate /dev/xvdb2 Physical volume "/dev/xvdb2" successfully created pvcreate /dev/xvdc1 Physical volume "/dev/xvdc1" successfully created
vgcreate mirrorvg /dev/xvdb1 /dev/xvdb2 /dev/xvdc1 Clustered volume group "mirrorvg" successfully created
vgs mirrorvg VG #PV #LV #SN Attr VSize VFree mirrorvg 3 0 0 wz--nc 68.97G 68.97G
lvcreate -l 1000 -m1 mirrorvg -n mirrorlv /dev/xvdb1:1-1000 /dev/xvdb2:1-1000 /dev/xvdc1:0 Logical volume "mirrorlv" created
lvs mirrorvg/mirrorlv LV VG Attr LSize Origin Snap% Move Log Copy% Convert mirrorlv mirrorvg mwi-a- 3.91G mirrorlv_mlog 47.00 lvs mirrorvg/mirrorlv LV VG Attr LSize Origin Snap% Move Log Copy% Convert mirrorlv mirrorvg mwi-a- 3.91G mirrorlv_mlog 91.00 lvs mirrorvg/mirrorlv LV VG Attr LSize Origin Snap% Move Log Copy% Convert mirrorlv mirrorvg mwi-a- 3.91G mirrorlv_mlog 100.00
May 10 14:52:52 doc-07 [19402]: Monitoring mirror device mirrorvg-mirrorlv for events May 10 14:55:00 doc-07 lvm[19402]: mirrorvg-mirrorlv is now in-sync
lvs -a -o +devices LV VG Attr LSize Origin Snap% Move Log Copy% Convert Devices mirrorlv mirrorvg mwi-a- 3.91G mirrorlv_mlog 100.00 mirrorlv_mimage_0(0),mirrorlv_mimage_1(0) [mirrorlv_mimage_0] mirrorvg iwi-ao 3.91G /dev/xvdb1(1) [mirrorlv_mimage_1] mirrorvg iwi-ao 3.91G /dev/xvdb2(1) [mirrorlv_mlog] mirrorvg lwi-ao 4.00M /dev/xvdc1(0)
lvs -a -o seg_pe_ranges --segments PE Ranges mirrorlv_mimage_0:0-999 mirrorlv_mimage_1:0-999 /dev/xvdb1:1-1000 /dev/xvdb2:1-1000 /dev/xvdc1:0-0
cman_tool services Service Name GID LID State Code Fence Domain: "default" 4 2 run - [1 2 3] DLM Lock Space: "clvmd" 12 7 run - [1 2 3] DLM Lock Space: "clustered_log" 14 9 run - [1 2 3] User: "usrm::manager" 10 4 run - [1 2 3]