CentOS 7.x Create LVM partition on new disk

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The below steps assume device name to be /dev/nda. In reality it might be /dev/sda or /dev/sdb for serial disks and /dev/xvda or /dev/xvdb for virtual disks, etc.

1. yum -y install lvm2
2. (Optional) Create partition to be used as physical volume. We can use entire disk for physical volume also. But creating partition seems like a good idea.

   fdisk /dev/nda
   #below on fdisk prompt
   n  #for new partition
   p  #for primary partition
   1  #for first primary partition
   #leave blank for default for first sector typically 2048
   #leave blank for default for last sector
   p  #print partition table
   t  #for changing partition type
   #automatically partition 1 will get selected, if that is the only partition
   8e #for Linux LVM
   w  #for save and quit

3. Rescan disk for kernel to learn the new partition

   partprobe /dev/nda

4. Create LVM physical volume on new partition

   pvcreate /dev/nda1

   On iSCSI volumes try /dev/disk/by-path/ based device names.

5. Create volume group using available physical partitions

   vgcreate vgtest /dev/nda1

   More than one physical volume can be part of same volume group. Thus to increase space we can add new disks, create physical volume on new disks and add new physical volume to existing vg using:

   vgextend vgtest /dev/ndb

6. Create logical volume as specific size or as percentage of VG size using:

   lvcreate -L 900M -n lvtest1 vgtest

   or

   lvcreate -l '100%VG' -n lvtest1 vgtest

   Later on if volume group is extended using 'vgextend' the lvm partition can be extended using 'lvextend' with similar -l or -L options. Example lvextend command is:

   lvextend -l '100%VG' --resizefs vgtest/lvtest1

   Here -l is for extents and -L is for size (eg 30GB)

   We can increase/decrease size by specific value by prefixing +/-. Eg to increase by 30GB we can use lvextend -L +30G <device>

   --resizefs is useful in avoiding separate step for resizing filesystem. We can increase both LVM and filesystem with a single step.

7. Display logical volume availability using:

   vgdisplay -v | grep LV | grep -i status

   If the status is *NOT available* then use following to activate vg

   vgchange -a y vgtest

   and validate that status changes to *available*

8. Create partition on newly created logical volume:

   mkfs.ext4 /dev/vgtest/lvtest1

   Use filesystems such as ext3 or ext4 or xfs that can be resized online, if kernel supports it. ext3 or ext4 can also be shrinked if not mounted. For resizing use:

   resize2fs /dev/vgtest/lvtest1

   For brtfs refer https://www.suse.com/support/kb/doc/?id=000018798 and for xfs use xfs_grow

9. For persistent mounting use /etc/fstab with UUID. For that list UUID with

   blkid

   and note UUID against /dev/mapper/vgtest-lvtest1.

10. Then add following to /etc/fstab

    UUID="XXX"	     /mnt/backups2      ext4    defaults  	0 0

    assuming above UUID, file-system and desired mount location of /mnt/backups2.

11. Finally test by mounting using:

    mount -a
    df -h | grep backup

    to validate whether /etc/fstab entry is correct or not.

For reverse shriking or reducing existing partition on top of LVM refer https://www.systutorials.com/124416/shrinking-a-ext4-file-system-on-lvm-in-linux/

Also see:

• CentOS 7.x Live extend size of ext4 on top of LVM without umount

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