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Understanding LVM In the early days of Linux servers, storage management relied on creating fixed partitions on disks. However, partitions posed limitations due to their lack of flexibility. When disk space needed adjustment, partitions could not be easily resized, leading to inefficiencies. To address this, Logical Volume Manager (LVM) was introduced, offering significant advantages in storage management. LVM Architecture LVM operates through several layers within its architecture. At the base layer, various storage devices such as disks, partitions, or LUNs (Logical Unit Numbers) from SANs are utilized. Best practice recommends using partitions as physical volumes (PVs) within LVM. This allows other tools to recognize pre-configured storage on the block device, minimizing configuration errors. Physical volumes are designated as part of a volume group (VG), which represents an abstracted pool of available storage. Unlike fixed allocations, volume groups are dynamic and can expand as needed by adding more physical volumes. This flexibility enables seamless adjustments to logical volumes (LVs) that are built upon the volume group. LVs do not interact directly with disks but draw storage from available space within the volume group. This setup permits a single logical volume to span multiple physical volumes, enhancing storage flexibility. File Systems and Flexibility Logical volumes host file systems, leveraging their flexibility to adjust file system sizes as needed. File systems associated with logical volumes can easily be extended or, if supported, reduced in size to optimize disk space usage. This dynamic resizing capability depends on the file system's inherent features and support for size adjustments. LVM Features LVM offers several compelling features that simplify storage management. Foremost among these is its ability to adapt to changing storage needs without the constraints of physical hard drives. By adding new physical volumes to a volume group, administrators can seamlessly expand logical volumes to meet increased storage demands. Moreover, LVM supports snapshots, which capture the current state of a logical volume, facilitating data recovery or backups without disrupting ongoing operations. Administrators appreciate LVM's capability to replace failing hardware efficiently. By using commands like pvmove, data can be transferred within the volume group, enabling the removal of faulty disks and adding new ones dynamically, all without downtime for the logical volumes. Creating LVM Logical Volumes Creating LVM logical volumes involves a systematic approach to establish the necessary layers: converting physical devices into physical volumes (PVs), aggregating PVs into volume groups (VGs), and creating logical volumes (LVs). Command-line utilities, which are universally accessible, provide straightforward tools for these operations. Tip for RHCSA Exam For those preparing for the RHCSA exam, familiarity with LVM commands—specifically pv, vg, and lv—is essential. These commands simplify management tasks and can be easily accessed via the command line. Using the --help option with any LVM command provides a concise summary of its usage, ensuring efficient execution of necessary operations. By understanding LVM's architecture and leveraging its features, administrators gain a robust framework for managing storage effectively across diverse Linux environments. Creating Physical Volumes for LVM To effectively utilize LVM tools for managing storage, begin by preparing partitions designated as LVM type. This process resembles typical partitioning methods outlined in before, with a crucial distinction: partitions must be flagged as LVM type before committing changes to disk. In utilities like fdisk and gdisk, use the t command from the menu to modify partition types. For MBR disks, set the type to 8e; for GUID disks, use 8e00. Alternatively, newer versions of fdisk support using lvm as a direct alias for LVM type. If using parted, within its interface, execute set n lvm on to mark a partition (where n denotes the partition number) for LVM use. After creating and marking the partition as LVM type, employ pvcreate to initialize it as a physical volume. This step writes essential metadata to the partition, enabling its integration into a volume group for subsequent storage management tasks. Exercise: Creating a Physical Volume To practice creating a physical volume, ensure your system has a hard disk with available unpartitioned space. Follow these steps, using /dev/sdd as an example: Open a root shell and execute fdisk /dev/sdd. Enter p to display the current partition table, confirming no partitions exist. Type g to initialize a GPT partition table. Press n to create a new partition, accepting defaults for partition number and sectors. Specify +1G when prompted for the last sector, creating a 1 GiB partition. Use t to change the partition type to lvm. Verify the partition creation with p. Repeat steps 4-7 to create additional 1 GiB LVM partitions if needed. Save changes and exit fdisk with w. Use lsblk to confirm the new partitions are created successfully. Execute pvcreate /dev/sdd1 to initialize /dev/sdd1 as an LVM physical volume. Verify the creation with pvs. Example: Creating an LVM Partition in fdisk [root@server1 ~]# fdisk /dev/sdd Welcome to fdisk (util-linux 2.37.4). Changes will remain in memory only, until you decide to write them. Be careful before using the write command. Command (m for help): g Created a new GPT disklabel (GUID: 3BCE8E49-EFDF-9144-ACD5-290F4FCCDA07). Command (m for help): n Partition number (1-128, default 1): First sector (2048-41943006, default 2048): Last sector, +/-sectors or +/-size{K,M,G,T,P} (2048-41943006, default 41943006): +1G Created a new partition 1 of type 'Linux filesystem' and of size 1 GiB. Command (m for help): t Selected partition 1 Partition type or alias (type L to list all): lvm Changed type of partition 'Linux filesystem' to 'Linux LVM'. Command (m for help): p Disk /dev/sdd: 20 GiB, 21474836480 bytes, 41943040 sectors Disk model: VMware Virtual S Units: sectors of 1 * 512 = 512 bytes Sector size (logical/physical): 512 bytes / 512 bytes I/O size (minimum/optimal): 512 bytes / 512 bytes Disklabel type: gpt Disk identifier: 3BCE8E49-EFDF-9144-ACD5-290F4FCCDA07 Device Start End Sectors Size Type /dev/sdd1 2048 2099199 2097152 1G Linux LVM Command (m for help): w The partition table has been altered. Calling ioctl() to re-read partition table. Syncing disks. Example: Verifying the Physical Volume [root@server1 ~]# pvcreate /dev/sdd1 Physical volume "/dev/sdd1" successfully created. [root@server1 ~]# pvs PV VG Fmt Attr PSize PFree /dev/sda2 rhel lvm2 a--

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