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Thin Provisioning

LVM thin provisioning allows you to over-provision the physical storage. You can create file systems which are larger than the available physical storage. LVM thin provisioning allows you to create virtual disks inside a thin pool. The size of the virtual disk can be greater than the available space in the thin pool. It is important that you monitor the thin pool and add more capacity when it starts to become full.

Configuring thinProvision volume

For creating thin-provisioned volume, use thinProvision parameter in storage class. It's allowed values are: "yes" and "no". If we don't use this parameter by default it's value will be "no" and it will work as thick provisioned volumes.

apiVersion: storage.k8s.io/v1
kind: StorageClass
metadata:
 name: lvm-sc
allowVolumeExpansion: true
provisioner: local.csi.openebs.io
parameters:
  volgroup: "lvmvg"
  thinProvision: "yes"

Before creating thin provision volume, make ensure that required thin provisioning kernel module dm_thin_pool is loaded on all the nodes.

To verify if the modules are loaded, run:

lsmod | grep dm_thin_pool

If modules are not loaded, then execute the following command to load the modules:

modprobe dm_thin_pool

Extend the Thin Pool size

Thin-pools are just a logical volume, so if we need to extend the size of thin-pool we can use the same command like, we have used for logical volumes extend, but we can not reduce the size of thin-pool.

$ lvextend -L +15G lvmvg/thin_pool
  Extending logical volume thin_pool to 30.00 GiB
  Logical volume mythinpool successfully resized

Configure Auto Extending of the Thin Pool (Configure Over-Provisioning protection)

  1. Since we automatically create thin pool as part of first thin volume provisioning, we need to enable the monitoring using lvchange command on the all thin pools across the nodes to use the auto extend threshold feature.

    To Ensure monitoring of the logical volume is enabled.

    $ lvs -o+seg_monitor
 LV             VG    Attr       LSize Pool           Origin Data%  Meta%  Move Log Cpy%Sync Convert Monitor
 lvmvg_thinpool lvmvg twi-aotz-- 2.07g                       0.00   11.52                            not monitored

    If the output in the Monitor column reports, as above, that the volume is not monitored, then monitoring needs to be explicitly enabled. Without this step, automatic extension of the logical thin pool will not occur, regardless of any settings in the lvm.conf.

    $ lvchange --monitor y lvmvg/lvmvg_thinpool

    Double-check that monitoring is now enabled by running the lvs -o+seg_monitor command a second time. The Monitor column should now report the logical volume is being monitored.

    $ lvs -o+seg_monitor
LV             VG    Attr       LSize Pool           Origin Data%  Meta%  Move Log Cpy%Sync Convert Monitor
lvmvg_thinpool lvmvg twi-aotz-- 2.07g                       0.00   11.52                            monitored

  2. Editing the settings in the /etc/lvm/lvm.conf can allow auto growth of the thin pool when required. By default, the threshold is 100% which means that the pool will not grow. If we set this to, 75%, the Thin Pool will autoextend when the pool is 75% full. It will increase by the default percentage of 20% if the value is not changed. We can see these settings using the command grep against the file.

    $ grep -E ‘^\s*thin_pool_auto’ /etc/lvm/lvm.conf 
thin_pool_autoextend_threshold = 100
thin_pool_autoextend_percent = 20