14.1 Introduction to the Logical Storage Manager

What follows is a brief introduction to the Logical Storage Manager. For more in depth information, see the Tru64 UNIX Logical Storage Manager Guide as well as the Tru64 UNIX File System Administration Handbook by Steve Hancock.

LSM is essentially RAID implemented in software. What is RAID? See Figure 14-1.

Figure 14-1: What is RAID?

LSM manages a pool of physical storage and allows you to divide that pool in a variety of ways to create virtual devices that are presented to the operating system as logical volumes. These logical volumes can be accessed via both block and character device special files located in the /dev/vol and /dev/rvol subdirectories respectively.

The CLSM subsystem sits atop the I/O Mapper and the Device Request Dispatcher (DRD) and below the file systems layer as illustrated in Figure 14-2.

Figure 14-2: Cluster Device I/O Subsystem Relationships

14.1.1 LSM Architecture

The LSM architecture is composed of four major components:

• Physical Disk

• Subdisk

• Plex

• Volume

Figure 14-3 shows how the various components interact.

Figure 14-3: Relationship of LSM Objects

14.1.1.1 Physical Disk

Physical disks are just what you think they are: hard disk drives. However, a physical disk in LSM terms...