Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010 Administration Manual

Contents

Novell LINUX ENTERPRISE SERVER 11 - STORAGE ADMINISTRATION GUIDE 2-23-2010 Administration Manual Manual pdf 28 page image

28 SLES 11: Storage Administration Guidenovdocx (en) 7 January 2010Figure 4-1 compares physical partitioning (left) with LVM segmentation (right). On the left side,one single disk has been divided into three physical partitions (PART), each with a mount point(MP) assigned so that the operating system can access them. On the right side, two disks have beendivided into two and three physical partitions each. Two LVM volume groups (VG 1 and VG 2)have been defined. VG 1 contains two partitions from DISK 1 and one from DISK 2. VG 2 containsthe remaining two partitions from DISK 2. In LVM, the physical disk partitions that are incorporatedin a volume group are called physical volumes (PVs). Within the volume groups, four logicalvolumes (LV 1 through LV 4) have been defined, which can be used by the operating system via theassociated mount points. The border between different logical volumes need not be aligned with anypartition border. See the border between LV 1 and LV 2 in this example.LVM features: Several hard disks or partitions can be combined in a large logical volume. Provided the configuration is suitable, an LV (such as /usr) can be enlarged when the freespace is exhausted. Using LVM, it is possible to add hard disks or LVs in a running system. However, this requireshot-swappable hardware that is capable of such actions. It is possible to activate a striping mode that distributes the data stream of a logical volume overseveral physical volumes. If these physical volumes reside on different disks, this can improvethe reading and writing performance just like RAID 0. The snapshot feature enables consistent backups (especially for servers) in the running system.With these features, using LVM already makes sense for heavily used home PCs or small servers. Ifyou have a growing data stock, as in the case of databases, music archives, or user directories, LVMis especially useful. It allows file systems that are larger than the physical hard disk. Anotheradvantage of LVM is that up to 256 LVs can be added. However, keep in mind that working withLVM is different from working with conventional partitions. Instructions and further informationabout configuring LVM is available in the official LVM HOWTO (http://tldp.org/HOWTO/LVM-HOWTO/).Starting from kernel version 2.6, LVM version 2 is available, which is downward-compatible withthe previous LVM and enables the continued management of old volume groups. When creatingnew volume groups, decide whether to use the new format or the downward-compatible version.LVM 2 does not require any kernel patches. It makes use of the device mapper integrated in kernel2.6. This kernel only supports LVM version 2. Therefore, when talking about LVM, this sectionalways refers to LVM version 2.4.2 Creating LVM PartitionsYou create an LVM partition by first clicking Create > Do not format then selecting 0x8E LinuxLVM as the partition identifier. After creating all the partitions to use with LVM, click LVM to startthe LVM configuration.4.3 Creating Volume GroupsIf no volume group exists on your system yet, you are prompted to add one (see Figure 4-2). It ispossible to create additional groups with Add group, but usually one single volume group issufficient. system is suggested as a name for the volume group in which the SUSE® LinuxEnterprise Server system files are located. The physical extent size defines the size of a physicalblock in the volume group. All the disk space in a volume group is handled in chunks of this size.