How to safely remove disk from LVM

Learn how to safely remove disk from LVM. Its useful when you need to free up disks from volume group and re-use somewhere else or replace faulty disk.

This article will serve solution for below questions :

• How to safely remove disk from LVM
• How to remove the disk from VG online
• How to copy data from one disk to other at the physical level
• How to replace a faulty disk in LVM online
• How to move physical extents from one disk to another
• How to free up disk from VG to shrink VG size
• How to safely reduce VG

We have volume group named vg01 which has 20M logical volume created in it and mounted it on /mydata mount point. Check lsblk output below –

Now, attach new disk of same or bigger size of disk /dev/xvdf. Identify new disk on the system by using lsblk command again and comparing the output to previous one.

You can see new disk has been identified as /dev/xvdg. Now, we will add this disk to current VG vg01. This can be done using vgextend command. Obviously, before using it in LVM you need to run pvcreate on it.

Now we have disk to be removed /dev/xvdf and new disk to be added /dev/xvdg in same volume group vg01. You can verify it using pvs command

Observe above output. Since we created 20M mount point from disk /dev/xvdf it has 20M less free size. The new disk /dev/xvdg is completly free.

Now, we need to move physical extents from disk xvdf to xvdg. pvmove is command used to achieve this. You just need to supply disk name from where you need to move out PE. Command will move PE out of that disk and write them to all available disks in the same volume group. In our case, only one other disk is available to move PE.

Move progress is shown periodically. If due to any reason operation interrupted in between then moved PE will remain at destination disks and un-moved PEs will remain on the source disk. The operation can be resumed by issuing the same command again. It will then move remaining PE out of the source disk.

You can even run it in background with nohup.

In above command, it will run pvmove in background. It will redirect normal console outputs in normal.log file under current working directory whereas errors will be redirected and saved in error.log file in current working directory.

Now if you check pvs output again, you will find all space on disk xvdf is free which means its not been used to store any data in that VG. This ensures you can remove the disk without any issues.

Before removing/detaching disk from server, you need to remove it from LVM. You can do this be reducing VG and opting that disk out.

Now disk xvdf can be removed/detached from server safely.

Few useful switches of pvmove :

Verbose mode prints more detailed information of operation. It can be invoked by using -v switch.

Interval at which command updates the progress can be changed. -i switch followed by number of seconds can be used to get updates from command on user defined intervals on progress.