Some of the important commands to verify (check) existing block devices, partitions and LVM details:

• To list current block device details including partitions
  lsblk
• to view details of existing volume group:
  vgscan
• alternatively (more details) use vgs command:
  vgs

Problem 1: Creating Logical Volume

You are required to create a logical volume of 300m, where volume group name should be vg1 and logical volume name should be vg1

1. Allocating partition for physical volume
   fdisk /dev/sdb #assuming that /dev/sdb don’t have partition yet, in my case i have verified it with lsblk command.
   • to print existing partition. In my case no partitions exist.
     choose p
   • To create new partition
     choose n
   • choose partition type (primary or logical):
     choose p
   • choose first secton
     press enter to choose default
   • choose last sector of partition. you can use +size{k,m,g}
     type +300m
   • you need to change file system type to Linux lvm
     press t and enter 8e
   • you need to save and exit
     press w
   • Now you are out of fdisk command, to you need to update kernel for changes in partition with partprobe command.
     partprobe
2. Creating physical volume (you can avoid this steps, creating volume group automatically creates physical volume if not already created):
   pvcreate /dev/sdb1
3. Creating volume group
   vgcreate vg1 /dev/sdb1
4. Creating logical volume
   lvcreate -n mylv1 -L 300m vg1
5. Creating file system
   mkfs.xfs /dev/vg1/mylv1
6. Mounting to /data
   echo “/dev/vg1/mylv1 /data xfs defaults 0 0″ >> /etc/fstab
   mount -a
   Note: using UUID will be the safer approach.

Problem 2: Extending a Logical Volume

You are required to extend mylv1 to 500mg total size.
or,
You are required to extend mylv1 with additional 200MB size.
or,
You are required to extend mylv1 with 50 additional extents (assuming default 4MB PE size)
or,
You are required to extend mylv1 to 125 total extents.

1. use pvs command to view details of pvs. If you don’t have additional space add another partition. In my case I have /dev/sdc1 (new disk)
   pvs
2. Create partition following step 1 in problem1.
   Note: As I have already mentioned that pvcreate is not requried, as vgcreate automatically calls it. I am skipping it.
3. Extending Volume group vg1
   vgextend vg1 /dev/sdc1
4. Extending logical volume
   lvextend -r -L +200m /dev/vg1/mylv1

   xfs_grow /dataalternatively,  you can use following command to extend the desire paritition to 500MB
   lvextend -r -L 500m /dev/vg1/mylv1
   or using -l (125 extent x 4MB = 500MB)
   lvextend -r -l 125 /dev/vg1/mylv1
   or, (adding 50×4=200m with existing size)
   lvextend -r -l +50 /dev/vg1/mylv1

Some related topics which are less important

• Changing vg details
  
  • To deactivate vgs
    vgchange -a n vg1
  • to activate
    vgchange –available y vg1
• Taking a backup using snapshots
  • to take snapshon use lvcreate with  -s option. I am using 50 extent which will be 200, if PE size is 4MB.
    lvcreate -s -l 50  -n backup_of_mylv1 /dev/vg1/mylv1