Logical Volume (LVM) Simply The Best Complete How To

Finding new hard disks and partitions without rebooting

I will give you three methods to choose from. Pick your favorite. :)

1. echo 1> /sys/class/block/sda/device/rescan

   1. sda is the disk you want to rescan.

2. for i in $(ls /sys/class/scsi_host/) ; do echo "- - -" > /sys/class/scsi_host/$i/scan ; done

3. echo 1 > /sys/class/scsi_device/0\:0\:0\:0/device/rescan

   1. ls /sys/class/scsi_device/ to find out all the SCSI addresses you have on your system. You have to change the command to fit your addresses and rerun it for each address. This format represents the SCSI addressing system, which follows. H:C:T:L (Host:Channel:Target:LUN)

Running partprobe after you have done your rescan never hurt anyone.

Add a new disk to LVM without using partitions

One thing I highly recommend is to try and use whole disks without partitions when you can, it will make your life as an administrator a lot easier. Let's say you have a logical volume you have to keep increasing, deleting the partition table is never fun and should be avoided. Instead just use whole disks that you can expand.

Step 1

Let's add the disk to the physical volume group that exists. If you need to create a new volume group, the instructions for that are later in the blog.

pvcreate /dev/vdb

Make sure to change vdb for the disk you want to add. A quick way to find the name of your new disk is the command lsblk. Let's check to see that it was successfully added. You use the pvs command to get a short summary about the disks in your physical volume group. To get more information use pvdisplay. The new disk should be listed.

Step 3

The next step is to add it to a current volume group, or create a new volume group if needed. If you don't know the name of your volume group, use vgs or vgdisplay to find it. To expand a current volume group.

vgextend rhel_redhat9 /dev/vdb

rhel_redhat9 is the name of the volume group you want to expand. Remember to change both the name of the volume group and the disk to your specifications. Let's verify that the volume group was increased by the size of the disk that was added to the physical volume group. Use vgs or vgdisplay to see that the volume group now has some free space that we can add to a logical volume group.

Step 4

The last step is to add that free space to a logical volume group. If you don't know the name of your logical volume group, use lvs or lvdisplay to find it. Let's add all the free space to our logical volume group.

lvextend -r -l +100%FREE /dev/rhel_redhat9/root

Remember that "rhel_redhat9" is your volume group, and "root" is your logical volume group. If you don't use the -r option, you need to manually extend the filesystem. Let's look at how we manually extend the filesystem on the mounted volume group. To see the filesystem type being used issue df -Th. I am running xfs, to use all of the available space. xfs_growfs /dev/mapper/rhel_redhat9-root

If you are running ext4, you can grow the filesystem with resize2fs.

Remember that it doesn't matter if you use the mapper path or not, both are symbolic links to the same thing.

Expand an LVM partition

Step 1

Let's use this setup as an example. We have the "vdc". This disk has four partitions. Partition 1, 3 and 4 are all using the "opt" volume group, and "lv_opt" logical volume group.

Step 2

Let's add 2GB to the 10GB "vdc" disk, and then expand the "vdc4" partition using all that extra space. Let's use fdisk since the disklabel type is dos for the "vdc" disc. If the disklabel type is gpt, use gparted instead of fdisk. You can see the disklabel type with fdisk -l

Step 3

fdisk /dev/vdc

Press "p" to print out the partition tables. Let's expand the last primary partition, "vdc4". Let's check the free unpartitioned space by pressing "F". If you are using an old version of fdisk, "F" will not be an option.

Here is the scary part, we must delete the partition and recreate it using the new size that we want. As you can see the vdc4 partition is 2G in size. Let's add 2GB to it and make it 4GB.

In fdisk, press "d" and select the partition you want to delete.

Let's re-create the partition by pressing "n." Press "enter" and select the default first sector. For me it's going to be a primary partition number 4 and I select the default first sector that is proposed.

The disk was originally 2GB and I want to add 2GB to the disk. I will write +4GB when it prompts me in the next step. If you want to use all of the space, just press "enter".

Last sector, +/-sectors or +/-size{K,M,G,T,P} (12584960-52428799, default 52428799): +4G

Then it asked me. "Do you want to remove the signature? [Y]es/[N]o:" I pressed N.

Since we are resizing a partition we must keep it.

Press "w" to write the information to disk. Now vdc4 has 4GB instead of 2GB.

Step 4

Let's add it to LVM.

pvresize /dev/vdc4

Let's verify the free space with pvs

If you run vgs you can see that the "ops" volume group now has free space since the vdc4 partition was allocated to the "ops" volume group.

Step 5

Now we extend the logical volume group "lv_opt".

lvextend -r -l +100%FREE /dev/opt/lv_opt

Step 6

If you didn't use the -r option to extend the

Grow the filesystem. xfs_growfs /dev/mapper/opt-lv_opt

Create a volume group and a logical volume group

Step 1

Add the disk or partition to the physical volume group. Change vdc1 for your disk/partition. pvcreate /dev/vdc1

Step 2

Let's create the volume group named "var" using /dev/vdc1.

vgcreate var /dev/vdc1

Step 3

Let's create the logical volume group named "lvdata" and use all of the space available from the "var" volume group we just created.

lvcreate -l 100%FREE -n lvdata var

Step 4

Now we need to add a filesystem to our logical volume.

mkfs.xfs /dev/var/lv_var

Step 5

Mount the filesystem. Change /tmp/var for whatever you are using.

mount /dev/var/lv_var /tmp/var/

Mount it using /etc/fstab if you want the mount to survive a reboot.

In /etc/fstab, this would mount the lv_var in the /tmp/var directory.

/dev/opt/lv_var /tmp/var xfs defaults 0 0

GPT Disks

Step 1

If you need to verify that you are using gpt, fdisk -l

You should see, "Disk label type: gpt"

If you see Dos, use another method above, not this one.

Let's start by scanning the SCSI bus. See the three methods above, pick one.

Step 2

gdisk -l /dev/vda

Change out vda for your disk.

"Total free space is ..." should list the free space.

Step 3

gdisk /dev/vda

Press "p" to print out your partition table.

Take note of Start (sector) and the End (sector) for the partition you want to expand.

Next, press "i", this will print out your "Partition unique GUID". You need to use it later so print it out now. Next we need to delete the partition. Press "d" and select the partition you want to expand.

Then press "n" and create a new partition.

Check to see if the "First sector" matches the "First sector" you saw when you printed out the partition tables. It should by default be fine, press Enter.

The "Last sector" should be different, a higher number than before. Compare it to the "Last Sector" when you printed out the partition tables. If you want to use all of the free space available just press enter. If you want to increase it by a specific amount type in +2GB or whatever you need.

Then it asks you about the filesystem type. Something like this:

Current type is 'Linux filesystem' Hex code or GUID (L to show codes, Enter = 8300):

We need to set it to LVM so press "L". Type in 8e00, you might need to do it twice.

Press "p" and verify that the partition size has increased.

Now press "x" to enter the "expert mode".

Press "c" to set the GUID to the old value. Copy and paste in the old GUID.

Next press "w", it will say, "Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING PARTITIONS!!"

Press "Y".

Step 4

Run partprobe and lsblk and you should see the increased size.

/dev/vda3 was increased by 10GiB.

Step 5

Last step is to increase the size in LVM.

pvresize /dev/vda3

Use pvs to see the "PFree". In my case it was 10GiB.

lvresize -r -l +100%FREE /dev/centos/root

Make sure to use the your vg and lv names.

df -Th Verify that your lvm has increased by the size you wanted.

Create a VG with a different physical extent

The default physical extent size is 4MB. If you want a larger physical extent you must do so when you create the VG. Let's say you want a VG with the name, data and the physical extent size should be 8MB.

vgcreate -s 8M data /dev/nvem0n1p2

Random Debug Information

Not all of the space available to /dev/sda appears to be used

• Warning: Not all of the space available to /dev/sda appears to be used, you can fix the GPT to use all of the space (an extra 10485760 blocks) or continue with the current setting? Fix/Ignore? This is fixed with parted -l

PVS Device not found on cloned machine

• If you have a machine that has been cloned. You might get this message when you run pvs Device files last seen on "device" not found. rm /etc/lvm/devices/system.devices and then vgimportdevices -a

Notes From YouTube

I said in my YouTube video that I would add the parted command I used.

parted /dev/sda mklabel gpt mkpart primary 1MB 2301MB