Appendix D. LVM Volume Group Metadata

Appendix D. LVM Volume Group Metadata

The configuration details of a volume group are referred to as the metadata. By default, an identical copy of the metadata is maintained in every metadata area in every physical volume within the volume group. LVM volume group metadata is small and stored as ASCII.

If a volume group contains many physical volumes, having many redundant copies of the metadata is inefficient. It is possible to create a physical volume without any metadata copies by using the --metadatacopies 0 option of the pvcreate command. Once you have selected the number of metadata copies the physical volume will contain, you cannot change that at a later point. Selecting 0 copies can result in faster updates on configuration changes. Note, however, that at all times every volume group must contain at least one physical volume with a metadata area (unless you are using the advanced configuration settings that allow you to store volume group metadata in a file system). If you intend to split the volume group in the future, every volume group needs at least one metadata copy.

The core metadata is stored in ASCII. A metadata area is a circular buffer. New metadata is appended to the old metadata and then the pointer to the start of it is updated.

You can specify the size of metadata area with the --metadatasize. option of the pvcreate command. The default size is too small for volume groups with many logical volumes or physical volumes.


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