< 1 Logical Volume Manager | Commands | 3 Volume Group Administration >

8. Linear Logical Volumes

https://www.udemy.com/course/a-complete-guide-on-linux-lvm/learn/lecture/13061988#overview

Creating the Volume Group

• Volume Group is a pool of the physical volumes (PVs)
• Volume Groups are divided into Logical Volumes
• Logical Volumes are allocated into (mapped to) the same size as the Physical extents (PE) [See Logical Volumes below]
  • 1 PE = 4MB
  • If PV1 (Physical Volume 1) = 100MB, there will be 25 (100/4) Physical Extents
  • If PV2 = 100MB, there will be 50 PE
  • VG1 (Volume Group 1) = PV1 + PV2, so 300MB = 75 PE.

Logical Volumes

• These can be used by your applications
• When PE are assigned to a Logical Volume, they change from PE to LE (Logical Extents)
  • If 1 PE = 4 MB, then 1 LE also = 4 MB (Always 1 to 1)

Different types of Logical Volumes

• Linear
  • These aggregate space from one or monre physical volumes into one logical volume.
    • If you have three 100GB disks, you can create a 300GB logical volume.
    • The physical storage is concatenated.

9. Volume Group Creation

Creating Volume Groups

After the Physical Volumes have been created, create the Volume Group

Commands

Find which volumes are available

fdisk -l

Display the Physical Volumes

pvdisplay /dev/sdxn

Example:

# pvdisplay /dev/sda3
--- Physical volume ---
PV Name /dev/sda3
VG Name XSLocalEXT-cc138e33-c171-6d3f-e559-f9649d47ad75
PV Size 196.97 GiB / not usable <13.32 MiB
Allocatable yes (but full)
PE Size 4.00 MiB
Total PE 50422
Free PE 0
Allocated PE 50422
PV UUID 14dfcf-uhNt-wav7-d1jH-hdOH-fGCr-nABNQi

Create Volume Groups

vgcreate <groupName> /dev/sdx1 /dev/sdx2 ...

Display Volume Groups

vgdisplay <-v> </dev/GROUPNAME>

-v: Show Physical Volume information

Example:

$ sudo vgdisplay
--- Volume group ---
VG Name XSLocalEXT-cc138e33-c171-6d3f-e559-f9649d47ad75
System ID 
Format lvm2
Metadata Areas 1
Metadata Sequence No 2
VG Access read/write
VG Status resizable
MAX LV 0
Cur LV 1
Open LV 1
Max PV 0
Cur PV 1
Act PV 1
VG Size 196.96 GiB
PE Size 4.00 MiB
Total PE 50422
Alloc PE / Size 50422 / 196.96 GiB
Free PE / Size 0 / 0 
VG UUID PQfRRm-HJvu-2L3r-ohPX-tWaj-azeD-mwIaxj

With -v

 --- Logical volume ---
LV Path /dev/XSLocalEXT-cc138e33-c171-6d3f-e559-f9649d47ad75/cc138e33-c171-6d3f-e559-f9649d47ad75
LV Name cc138e33-c171-6d3f-e559-f9649d47ad75
VG Name XSLocalEXT-cc138e33-c171-6d3f-e559-f9649d47ad75
LV UUID PpOE7h-qUkF-grNR-2zxi-GMZC-S9HQ-mKhJY6
LV Write Access read/write
LV Creation host, time citrix01, 2020-04-06 17:42:57 -0500
LV Status available
# open 1
LV Size 196.96 GiB
Current LE 50422
Segments 1
Allocation inherit
Read ahead sectors auto
- currently set to 256
Block device 253:0

--- Physical volumes ---
PV Name /dev/sda3 
PV UUID 14dfcf-uhNt-wav7-d1jH-hdOH-fGCr-nABNQi
PV Status allocatable
Total PE / Free PE 50422 / 0

10 – 12. Practice Sessions and Command review

These are all Commands

13. Striped Logical Volumes

https://www.udemy.com/course/a-complete-guide-on-linux-lvm/learn/lecture/13062136#overview

Just like a RAID array, this is good for high I/O

Example 1:  The following command creates a striped volume across 2 PVs (-i) with a stripe of 64KB (-I).  The logical volume is 50GB (-L) named strpvol (-n) and is carved out of VG vglab.

• The default stripe size is 64kB.  If a number is submitted, it will be assumed to be kB

lvcreate -L -i 2 -I 64 -n strpvol vglab

Example 2: Specify the exact extents to use in your Logical Volume striped array

lvcreate -l 100 -i 2 -n strpvol /dev/dec1:0-49 /dev/ded1:50-99

14. Demonstration for Section 13.