User manual REDHAT ENTERPRISE LINUX 5.1 LVM ADMINISTRATION

[. . . ] Red Hat Enterprise Linux 5. 1 Cluster Logical Volume Manager LVM Administrator's Guide Cluster Logical Volume Manager Red Hat Enterprise Linux 5. 1 Cluster Logical Volume Manager LVM Administrator's Guide Edition 1. 0 Copyright © 2007 Red Hat Inc. . This material may only be distributed subject to the terms and conditions set forth in the Open Publication License, V1. 0 or later with the restrictions noted below (the latest version of the OPL is presently available at http://www. opencontent. org/openpub/). Distribution of substantively modified versions of this document is prohibited without the explicit permission of the copyright holder. Distribution of the work or derivative of the work in any standard (paper) book form for commercial purposes is prohibited unless prior permission is obtained from the copyright holder. [. . . ] After you export the volume group, the physical volume will show up as being in an exported volume group when you execute the pvscan command, as in the following example. [root@tng3-1]# pvscan PV /dev/sda1 is in exported VG myvg [17. 15 GB / 7. 15 GB free] PV /dev/sdc1 is in exported VG myvg [17. 15 GB / 15. 15 GB free] PV /dev/sdd1 is in exported VG myvg [17. 15 GB / 15. 15 GB free] . . . When the system is next shut down, you can unplug the disks that constitute the volume group and connect them to the new system. When the disks are plugged into the new system, use the vgimport command to import the volume group, making it accessible to the new system. Activate the volume group with the -a y argument of the vgchange command. 25 Chapter 4. Recreating a Volume Group Directory To recreate a volume group directory and logical volume special files, use the vgmknodes command. This command checks the LVM2 special files in the /dev directory that are needed for active logical volumes. You can incorporate the vgmknodes command into the vgscan command by specifying the -mknodes argument to the command. 4. 4. Logical Volume Administration This section describes the commands that perform the various aspects of logical volume administration. 4. 4. 1. Creating Logical Volumes To create a logical volume, use the lvcreate command. You can create linear volumes, striped volumes, and mirrored volumes, as described in the following subsections. If you do not specify a name for the logical volume, the default name lvol# is used where # is the internal number of the logical volume. The following sections provide examples of logical volume creation for the three types of logical volumes you can create with LVM. 4. 4. 1. 1. Creating Linear Volumes When you create a logical volume, the logical volume is carved from a volume group using the free extents on the physical volumes that make up the volume group. Normally logical volumes use up any space available on the underlying physical volumes on a next-free basis. Modifying the logical volume frees and reallocates space in the physical volumes. The following command creates a logical volume 10 gigabytes in size in the volume group vg1. lvcreate -L 10G vg1 The following command creates a 1500 megabyte linear logical volume named testlv in the volume group testvg, creating the block device /dev/testvg/testlv. lvcreate -L1500 -ntestlv testvg The following command creates a 50 gigabyte logical volume named gfslv from the free extents in volume group vg0. lvcreate -L 50G -n gfslv vg0 26 Creating Logical Volumes You can use the -l argument of the lvcreate command to specify the size of the logical volume in extents. You can also use this argument to specify the percentage of the volume group to use for the logical volume. The following command creates a logical volume called mylv that uses 60% of the total space in volume group testvol. lvcreate -l 60%VG -n mylv testvg You can also use the -l argument of the lvcreate command to specify the percentage of the remaining free space in a volume group as the size of the logical volume. The following command creates a logical volume called yourlv that uses all of the unallocated space in the volume group testvol. lvcreate -l 100%FREE -n yourlv testvg You can use -l argument of the lvcreate command to create a logical volume that uses the entire volume group. Another way to create a logical volume that uses the entire volume group is to use the vgdisplay command to find the "Total PE" size and to use those results as input to the the lvcreate command. The following commands create a logical volume called mylv that fills the volume group named testvg. # vgdisplay testvg | grep "Total PE" Total PE 10230 # lvcreate -l 10230 testvg -n mylv The underlying physical volumes used to create a logical volume can be important if the physical volume needs to be removed, so you may need to consider this possibility when you create the logical volume. For information on removing a physical volume from a volume group, see Section 4. 3. 5, "Removing Physical Volumes from a Volume Group". [. . . ] As another example, consider a situation where every machine in the cluster has the following entry in the configuration file: tags { hosttags = 1 } If you want to activate vg1/lvol2 only on host db2, do the following: 1. This solution involves storing hostnames inside the volume group metadata. 86 Appendix D. LVM Volume Group Metadata The configuration details of a volume group are referred to as the metadata. By default, an identical copy of the metadata is maintained in every metadata area in every physical volume within the volume group. [. . . ]