Linux Tutorials - Herong's Tutorial Examples - v5.37, by Dr. Herong Yang
Create LV on VG on the Fly
Describes what is a LV (Logical Volume) - A virtual storage partition in a VG (Volume Group) managed by the LVM. A tutorial example is given on how to create a new LV on a VG.
What Is LV (Logical Volume)? LV represents a virtual storage partition in a VG (Volume Group) managed by the LVM (Logical Volume Manager). A LV can be formatted into a specific file system.
There are a number commands provided on CentOS 8 systems for you to create and manage PVs.
1. List all LVs that are currently managed by LVM using the "lvs" command, which is a also sub-command of the "lvm" command. The output shows that I have 3 LVs named hosted on the "cl" VG.
herong$ sudo lvs LV VG Attr LSize Pool Origin Data% Meta% ... home cl -wi-ao---- 138.94g root cl -wi-ao---- 50.00g swap cl -wi-ao---- 7.71g
2. Display details of each LV using the "lvdisplay" command, which is also a sub-command of the "lvm" command. The output shows the VG's format is "lvm2".
herong$ sudo lvdisplay --- Logical volume --- LV Path /dev/cl/swap LV Name swap VG Name cl LV UUID gMCDUY-Ew9v-OFBj-pOuq-lZ27-... LV Write Access read/write LV Creation host, time localhost, 2020-03-27 05:01:49 +0800 LV Status available # open 2 LV Size 7.71 GiB Current LE 1974 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 253:1 --- Logical volume --- LV Path /dev/cl/home LV Name home VG Name cl LV UUID GTeo46-cl6I-XFL8-tCvb-vCeN-... LV Write Access read/write LV Creation host, time localhost, 2020-03-27 05:01:49 +0800 LV Status available # open 1 LV Size 138.94 GiB Current LE 35569 Segments 2 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 253:2 ...
As you can see from the output, a LV has 3 identities:
How To Create a New LV on a VG? If you have free spaces on a VG, you create a new LV using the "lvcreate" command.
1. Check free space on VG. I see "data" VG has 93 GiB of free space.
herong$ sudo vgs VG #PV #LV #SN Attr VSize VFree cl 2 3 0 wz--n- 1.00t 831.69g data 1 0 0 wz--n- 93.13g 93.13g
2. Create a new PV called "hr" with 10GiB on "data" using "lvcreate" command.
herong$ sudo lvcreate -L 10G -n hr data Logical volume "hr" created. herong$ sudo lvdisplay --- Logical volume --- LV Path /dev/data/hr LV Name hr VG Name data LV UUID 2upNkI-v5p8-ctQZ-mBPD-CmKC-... LV Write Access read/write LV Status available # open 0 LV Size 10.00 GiB Current LE 2560 Segments 1 Allocation inherit Read ahead sectors auto - currently set to 8192 Block device 253:3
3. Check the device path of the new LV using "file -s" command. The new LV is not formatted with file system yet and can be used as "data" device, also called "byte" device.
... herong$ sudo file -s /dev/data/hr /dev/data/hr: symbolic link to ../dm-3 herong$ sudo file -s /dev/dm-3 /dev/dm-3: data
4. Create an "ext4" file system on the LV using "mkfs" command.
herong$ sudo mkfs -t ext4 /dev/data/hr mke2fs 1.44.6 (5-Mar-2019) Creating filesystem with 2621440 4k blocks and 655360 inodes Filesystem UUID: b560da43-52a3-41c4-98a9-... Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632 Allocating group tables: done Writing inode tables: done Creating journal (16384 blocks): done Writing superblocks and filesystem accounting information: done herong$ sudo file -s /dev/dm-3 /dev/dm-3: Linux rev 1.0 ext4 filesystem data, UUID=b560da43-52a3-...
5. Mount the file system on the LV. I see new file system path, /dev/mapper/data-hr, is given to the LV.
herong$ sudo mount /dev/data/hr /mnt/temp herong$ ls -l /mnt/temp total 16 drwx------. 2 root root 16384 Mar 22 14:20 lost+found herong$ df Filesystem 1K-blocks Used Available Use% Mounted on /dev/mapper/data-hr 10255636 36888 9678076 1% /mnt/temp
Cool. I have successfully create a LV on a VG, and formatted it as an "ext4" file system.
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