Shared LVM overview
A key element of any PowerHA® SystemMirror® cluster is the data used by the highly available applications. This data is stored on AIX® LVM entities. PowerHA SystemMirror clusters use the capabilities of the LVM to make this data accessible to multiple nodes.
In a PowerHA SystemMirror cluster, the following definitions are used:
- A shared volume group is a volume group that resides entirely on the external disks shared by cluster nodes.
- A shared physical volume is a disk that resides in a shared volume group.
- A shared logical volume is a logical volume that resides entirely in a shared volume group.
- A shared file system is a file system that resides entirely in a shared logical volume.
As a system administrator of a PowerHA SystemMirror cluster, you may be called upon to perform any of the following LVM-related tasks:
- Creating a new shared volume group
- Extending, reducing, changing, or removing an existing volume group
- Creating a new shared logical volume
- Extending, reducing, changing, or removing an existing logical volume
- Creating a new shared file system
- Extending, changing, or removing an existing file system
- Adding, removing physical volumes.
When performing any of these maintenance tasks on shared LVM components, make sure that ownership and permissions are reset (on logical volumes) when a volume group is exported and then re-imported. After exporting and importing, a volume group is owned by root and accessible by the system group. Applications, such as some database servers that use raw logical volumes may be affected by this if they change the ownership of the raw logical volume device. You must restore the ownership and permissions to what is needed after this sequence.