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What are Users and Groups in Linux

What Are Users and Groups?
In addition to a Red Hat Enterprise Linux system having a username for each user allowed access to a system, each system has user groups. A user group is a group of one or more users. A user can be a member of more than one group.
User groups can be any grouping of users on which you decide: groups of users in a functional department, groups in the same physical location, or groups based on security access. It is important to plan the user groups for your company carefully before implementing them because changing them means changing the groups associated with files, which can sometimes lead to incorrect group permissions if they are not changed correctly.

RHEL-6 LVM Introduction Part 2

RHEL-6 LVM Introduction Part1

Creating a Physical LVM

Creating a Physical Volume
To create a new physical volume from free hard drive space or a hard drive partition, use the pvcreate command:
pvcreate <disk>
Replace <disk> with the device name of the hard drive:
pvcreate /dev/sda
or the partition name:
pvcreate /dev/sda1
The <disk> specified can also be a meta device or loopback device, but using an entire hard disk or partition is more common. After creating a physical volume, you can either add it to an existing volume group or create a new volume group with the physical volume.

Adding Additional Disk Space LVM

Adding Additional Disk Space

One big advantage of using LVM is that the size of a logical volume can be increased and logical volumes can be added to create additional mount points. To modify the LVM configuration post-installation, the lvm2 package needs to be installed.

To increase the size of an existing logical volume or to add a logical volume, you first need free disk space. This free disk space can either be disk space that already exists in the system as unpartitioned space (not part of an existing logical volume), an unused partition, physical volume that is not already a member of a logical volume, or disk space as a result of installing one or more additional hard drives to the system. The disk space can come from removing a logical volume to create space in the logical volume group, however, this is not common because if the LV already exists, it is most likely already being used and cannot be easily deleted without losing data.

What is LVM (logical Volume manager)

Understanding LVM (logical Volume manager)
Logical Volume Manager, or LVM, is a storage management solution that allows administrators to divide hard drive space into physical volumes (PV), which can then be combined into logical volume groups (VG), which are then divided into logical volumes (LV) on which the file system and mount point are created.
A logical volume group can include more than one physical volume, a mount point can include more than one physical hard drive, meaning the largest mount point can be larger than the biggest hard drive in the set. These logical volumes can be resized later if more disk space is needed for a particular mount point. After the mount points are created on logical volumes, a filesystem must be created on them.

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