Troubleshooting Logical Volume Manager boot problems

When your server boots up, it normally self-scans for LVM volumes. It does so by executing the pvscan command from the startup scripts, regardless of which Linux distribution you use. If something isn't working properly, however, pvscan will fail and you'll have to initialize LVM yourself. Once you understand how LVM works, this task isn't too onerous .

LVM's bottom layer consists of physical devices, or storage devices that are marked as usable by LVM. But not every storage device is a physical device; they need to be initialized using the pvcreate command before they can be used. When your server boots, it uses the pvscan command to find LVM devices that exist on your storage devices.

LVM's second layer consists of the volume groups. A volume group is a collection of one or more storage devices from which logical volumes can be created. During the configuration of LVM, one or more volume groups is normally created using the vgcreate command. When booting, your server uses the vgscan command to activate the volume group.

From the volume group, logical volumes are created. These are the storage devices on which file systems can be created. You use lvcreate to create them and ...

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lvscan to activate them. Figure 1 gives an overview of the LVM setup.

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Figure 1: Overview of LVM setup

Before you begin troubleshooting, inspect your volumes with the lvdisplay command. If all is well, lvdisplay will give an overview of your logical volumes. If it isn't, it will tell you, "No volume groups found." If this message is returned, you must check the LVM setup from the physical volumes up to the logical volumes to see what might be wrong. Use these steps to help with your troubleshooting:

1. If your LVM structure has never worked, start by checking the storage devices themselves. If you've added partitions to the LVM setup, the partition should be marked as partition type 8e. You can check with the fdisk command if this is the case: Use . If it isn't set to type 8e, use to open fdisk on your server's hard drive. Type t, followed by the number of the partition whose type you want to change. Finally, enter 8e, save the settings and reboot. If the problem was in the wrong partition type, your LVM volumes will be accessible after this fix.
2. If your volumes are still not accessible, use the pvdisplay command to indicate whether the storage devices are marked as LVM devices. If they are not but you believe you set them up as LVM devices previous, use . If this doesn't display your physical volumes, use to set up your storage device as an LVM device. Listing 1 shows you the result that pvdisplay and pvscan would normally return.

   Listing 1: Use pvscan to initialize existing physical volumes.
   

3. The next step is to repeat the preceding actions for the volume groups on your server. First use the vgdisplay command to see your current volume groups. If that doesn't give you a result, use vgscan to tell the server to scan for volume groups on your storage devices. Listing 2 shows the result of these commands:

   Listing 2: To initialize volume groups, use vgscan and vgdisplay.
   

At this point, your logical volumes should be accessible. If they are not, you have to start troubleshooting a problem unrelated to the boot procedure, which is an issue I will address in a later tip.

ABOUT THE AUTHOR: Sander van Vugt is an author and independent technical trainer, specializing in Linux since 1994. Vugt is also a technical consultant for high-availability (HA) clustering and performance optimization, as well as an expert on SLED 10 administration.

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