Day 38th: LVM Logical Volume Management for Linux

Small Q: books are the nourishment of the whole world. There is no book in life, just as there is no sunshine;

Books, as if the birds had no wings. --Shakespeare

=============================== Introduction =================================

LVM: Logical Volume Manager (Logical Volume management), which is a mechanism for managing disk partitions in a Linux environment

Why: Every Linux user will encounter this dilemma when installing Linux: How to accurately evaluate the LVM model when partitioning the system

Allocate the capacity of each hard disk partition, as the system administrator takes into account not only the capacity required for the current partition, but also the

Maximum number of capacity that may be required after partitioning. Because if the estimate is inaccurate, when a partition is not sufficient, the administrator may

To back up the entire system, clear the hard disk, re-partition the hard disk, and then restore the data to the new partition.

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Volume Group Volume Group (VG)

The volume group is the highest abstraction layer in LVM and is a memory pool composed of one or more PV.

Physical Volume Physical volume (PV)

A typical physical volume is a hard disk partition, or it can be an entire hard disk or a software RAID volume that has been created, and is the basic storage logic block of LVM.

Contains management parameters that are related to LVM.

Physical Block physical extent (PE)

Physical volumes are stored in units of equal size, the size of which is the same size as the logical volume block in the volume group, and the default is 4MB, so PV

Consists of a basic unit PE of equal size.

Logic Block logical extent (LE)

Logical volumes are stored in "blocks", and the block size of all logical volumes in a volume group is the same. Le is the same size as PE.

Logical Volume Logical Volume (LV)

The logical volume is equivalent to a partition in a non-LVM system, which is established on the VG and is a standard block device on which the file system can be built

Linear mapping

Linear mapping-assigns a range of physical blocks sequentially to logical volumes, such as the LV's LE 1-99 mapping to the Pv1,le 100-347 map

To PV2.

Interleaved mode

Interleaved mode-The logical blocks will be interleaved into different physical volumes, such as the LV's LE 1 mapped to PV1 Pe1,le 2 mapped to PV2 Pe1,le 3 mapped to PV1 PE2: This approach can improve the performance of logical volumes, but the logical volumes created in this way will not

Can be extended in the physical volume in which they reside.

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============================== Create LVM ================================

The first step is to create the physical file system

Command: fdisk/dev/sdb--create a physical volume and modify the ID to 8e

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The second step initializes the physical volume to PV

Create PV, add several file systems, and then add a RAID file system

Command: pvcreate/dev/sdb{5,6,7,8,9} ———— Add File system to PV

Pvcreate/dev/md0 ———— Add raid file system to PV

Pvs,pvdisplay ———— View System existing PV

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Step three create Volume group VG

Add PV to Volume Group, create VG volume group

Command: vgcreate [-s=16m] Test_vg/dev/sdk1/dev/sdl1

Specifies the PE size of the VG volume group name to be added to the VG in PV

Use man to help you see how it's Used

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Looking at the example above, we add PV to the volume group to create the VG

Command: Vgcreate vg0/dev/sdb{5,6,7,8,9}/dev/md0

Vgs,vgdisplay

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Note: The contents of [-s=16m] are optional, modify the default PE unit size, default is 4M, the largest volume group is 256G, modify the defaults

Unit is 16M and the largest volume group unit is 1024G

Command: Vgdisplay TESTVG | grep "Total PE"

Take a look at the default PE size of 4M,PV is 6, the total size of VG is 6.7.G

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Some operations for other VG volume groups

Activate VG

The VG and LV are inaccessible until they are activated.

Use man to help you look.

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Command: vgchange-a y vg0--activating vg0 Volume Group

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Hibernate the VG0 volume group when the VG is no longer used

Command: vgchange-a n vg0--make it no longer available

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Remove VG

Verify that no logical volumes are in the volume group before removing a volume group

Command: vgchange-a n vg0 ———— Dormant volume group

Vgremove vg0 ———— Remove the volume group

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Add new PV for VG

When the volume group space is low, you can add a new physical volume to enlarge the VG Volume group capacity, when the command is available vgextend

pvcreate/dev/sdb15--initializing Sdb15 to PV

Vgextend vg0/dev/sdb15--Add sdb15 to the volume group Vg0

Where/dev/sdb15 is the new PV, of course, before this, it should be initialized with Pvcreate

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Removing PV from VG

Before removing PV, you should confirm that PV is not used by LV

Command: pvdisplay/dev/sdb15--to see if PV is used

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If this PV is still in use, after confirming that it has not been used, the command vgreduce can be used to remove it from the VG.

Command: Vgreduce vg0/dev/sdb15 ———— remove PV from VG

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If there is data on the PV, the data should be transferred to other PV

Note: To remove a PV from the VG, the data from all active PE on it should first be transferred to the other PV, and the new PV must be part of this VG, there is enough space, such as to move the data on the pv1:/dev/md0 to PV2:/DEV/SDB6 available, It is recommended that the data in the LV be backed up before the data is transferred, and if the LV above the PV is interleaved, the transfer process cannot be interrupted.

Command: PVMOVE/DEV/MD0/DEV/SDB6

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Day 38th: LVM Logical Volume Management for Linux