Do you need lvm in linux?

Linux uses lvm. LVM refers to logical volume management, which is a mechanism for managing disk partitions in the Linux environment. LVM is a logical layer built on the hard disk and partitions to improve the flexibility of disk partition management. The biggest feature of LVM is that it can dynamically manage disks. Because the size of the logical volume can be dynamically adjusted without losing existing data; if a new hard disk is added, it will not change the existing upper logical volume. As a dynamic disk management mechanism, logical volume technology greatly improves the flexibility of disk management.

Introduction to LVM

LVM is the abbreviation of Logical Volume Manager. It is a mechanism for managing disk partitions in the Linux environment. LVM is built on A logical layer above hard disks and partitions to improve the flexibility of disk partition management.

The working principle of LVM is actually very simple. It abstracts and encapsulates the underlying physical hard disk and then presents it to upper-layer applications in the form of logical volumes. In the traditional disk management mechanism, our upper-layer application directly accesses the file system to read the underlying physical hard disk. In LVM, it encapsulates the underlying physical hard disk. When we read the underlying physical hard disk, When operating, it no longer operates on partitions, but performs underlying disk management operations through something called a logical volume. For example, if I add a physical hard disk, the upper-layer service will not be aware of it at this time, because it is presented to the upper-layer service in the form of a logical volume.

The biggest feature of LVM is that it can dynamically manage disks. Because the size of the logical volume can be dynamically adjusted without losing existing data. If we add a new hard disk, it will not change the existing upper logical volume. As a dynamic disk management mechanism, logical volume technology greatly improves the flexibility of disk management.

Basic logical volume management concepts:

• PV (Physical Volume) - Physical Volume
  The physical volume is in the logical volume management At the lowest level, it can be the partition on the actual physical hard disk, the entire physical hard disk, or the raid device.

• VG (Volumne Group) - Volume Group
  A volume group is built on a physical volume. A volume group must include at least one physical volume. After the volume group is created, it can be dynamic Add physical volumes to the volume group. A logical volume management system project can have only one volume group or multiple volume groups.

• LV (Logical Volume) - Logical Volume
  Logical volumes are built on volume groups. The unallocated space in the volume groups can be used to create new logical volumes. Logical volumes Once established, the space can be expanded and reduced dynamically. Multiple logical volumes in the system can belong to the same volume group or to multiple different volume groups.

• PE (Physical Extent) - Physical block

  LVM uses 4MB PE block by default. The LVM LV can only contain up to 65534 PEs (lvm1 format), so the default LVM LV maximum capacity is 4M*65534/(1024M/G)=256G. PE is the smallest storage block of the entire LVM. In other words, our data is actually processed by writing to PE. Simply put, this PE is a bit like the block size in the file system. Therefore, adjusting PE will affect the maximum capacity of LVM! However, after CentOS 6.x, this limitation no longer exists due to the direct use of various format functions of lvm2.

Operation process

1. Add two hard disks to the virtual machine

2. Use pvcreate to create a physical volume PV, and use pvs to view information or pvdisplay to view detailed information

3. Create a volume group VG

Use vgcreate to create a volume group VG, and here you can specify the size of the PE (LE) with the -s option, (default PE size 4M)

4. Create a logical volume LV

Use lvcreate to create the LV. lvcreate -n lvname -L lvsize(M,G) vgname

##5. Formatting and mounting

6. Logical volume expansion

After confirming that there is excess space In this case, use the lvextend command to extend the size of the logical volume LV

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