In one of my current projects I have to attach a (virtual) disk to a (cloud) server.
Gather information
To get an overview of the system I used this commands:
pvs pvdisplay vgs vgdisplay lvs lvdisplay fdisk -c -l /dev/sdb
Interpretation of information
| Physical Volume | Partition | Volume Group | Logical Volumes | Size |
| /dev/sda | 107 GB | |||
| /dev/sda | /dev/sda1 | 0,5 GB | ||
| /dev/sda | /dev/sda2 | 106,5 GB | ||
| /dev/sda | /dev/sda2 | vg00 | <99.50g | |
| /dev/sda | /dev/sda2 | vg00 | lv_home | 2 GB |
| /dev/sda | /dev/sda2 | vg00 | lv_usr | 2 GB |
| /dev/sda | /dev/sda2 | vg00 | "free" | <76.50g |
| /dev/sdb | 107 GB | |||
Technically it is possible to create a new logical volume inside volume group vg00, because there are > 76,5 GB unassigned and free storage.
But the vg00 is reserved for the Operating System and should not used for data from application.
Therefore the additional disk is needed for applicatin data.
Volume creation
Physical Volume with ~ 100 GB is attached to the server and added as /dev/sdb.
A volume group "vg_app" will be created with two logical volumes. One logical volume for logfiles, named "lv_logs" with 20 GB and the other with remaining free space, named "lv_app", for application data.
# create volume group vgcreate -s 32M vg_app /dev/sdb # create logical volume for logfiles lvcreate -L 20G -n lv_log vg_app # create logical volume for application data lvcreate -l 100%VG -n lv_app vg_app # show information vgdisplay -v /dev/vg_app mount -a
| Physical Volume | Volume Group | Logical Volume | Size |
| /dev/sdb | 107 GB | ||
| /dev/sdb | vg_app | 107 GB | |
| /dev/sdb | vg_app | lv_log | 20 GB |
| /dev/sdb | vg_app | lv_app | > 79 GB |
Create File system
mkfs -t ext4 /dev/vg_app/lv_app mkfs -t ext4 /dev/vg_app/lv_log
Mount logical volumes
mkdir /app mkdir /app/log mount /dev/mapper/vg_app-lv_log /app/log mount /dev/mapper/vg_app-lv_app /app mount -a vi /etc/fstab mount -a
# /etc/fstab # [...] existing files code [...] /dev/mapper/vg_app-lv_app /app ext4 defaults 0 0 /dev/mapper/vg_app-lv_log /app/log ext4 defaults 0 0
Test
Reboot and doublecheck that mounted volumes are still there.
reboot now ########## df -h Filesystem Size Used Avail Use% Mounted on [...] /dev/mapper/vg_app-lv_app 79G 57M 75G 1% /app /dev/mapper/vg_app-lv_log 20G 45M 19G 1% /app/log
-> Both logical volumes are mounted --> Success!