HP Serviceguard manual About Device File Names Device Special Files, Examples of Mirrored Storage

redundant storage in hardware. Two types of mirroring are RAID1 and RAID5. Here are some differences between the two storage methods:

•If you are using JBODs, the basic element of storage is an individual disk. This disk must be paired with another disk to create a mirror (RAID1). (Serviceguard configurations usually have separate mirrors on different storage devices).

•If you have a disk array, the basic element of storage is a LUN, which already provides storage redundancy via hardware RAID1 or RAID5.

About Device File Names (Device Special Files)

HP-UX releases up to and including 11i v2 use a naming convention for device files that encodes their hardware path. For example, a device file named /dev/dsk/c3t15d0 would indicate SCSI controller instance 3, SCSI target 15, and SCSI LUN 0. HP-UX 11i v3 introduces a new nomenclature for device files, known as agile addressing (sometimes also called persistent LUN binding).

Under the agile addressing convention, the hardware path name is no longer encoded in a storage device’s name; instead, each device file name reflects a unique instance number, for example /dev/[r]disk/disk3, that does not need to change when the hardware path does.

Agile addressing is the default on new 11i v3 installations, but the I/O subsystem still recognizes the pre-11.i v3 nomenclature. This means that you are not required to convert to agile addressing when you upgrade to 11i v3, though you should seriously consider its advantages.

For instructions on migrating a system to agile addressing, see the white paper LVM Migration from Legacy to Agile Naming Model at http://www.hp.com/go/hpux-core-docs.

NOTE: It is possible, though not a best practice, to use legacy DSFs (that is, DSFs using the older naming convention) on some nodes after migrating to agile addressing on others; this allows you to migrate different nodes at different times, if necessary. For information on migrating cluster lock volumes to agile addressing, see “Updating the Cluster Lock Configuration” (page 295).

For more information about agile addressing, see following documents in the 11i v3 collection at http://www.hp.com/go/hpux-core-docs:

•the Logical Volume Management volume of the HP-UXSystem Administrator’s Guide

•the HP-UX 11i v3 Installation and Update Guide

•the white papers:

◦Overview: The Next Generation Mass Storage Stack

◦HP-UX 11i v3 Persistent DSF Migration Guide

◦LVM Migration from Legacy to Agile Naming Model

◦HP-UX 11i v3 Native Multi-Pathing for Mass Storage

See also the HP-UX 11i v3 intro(7) manpage, and“About Multipathing” (page 33).

NOTE: As of A.11.20, Serviceguard supports cluster-wide DSFs, and HP recommends that you use them. See “About Cluster-wide Device Special Files (cDSFs)” (page 104).

Examples of Mirrored Storage

Figure 29 shows an illustration of mirrored storage using HA storage racks. In the example, node1 and node2 are cabled in a parallel configuration, each with redundant paths to two shared storage devices. Each of two nodes also has two (non-shared) internal disks which are used for the root file system, swap etc. Each shared storage unit has three disks, The device file names of the three disks on one of the two storage units are c0t0d0, c0t1d0, and c0t2d0. On the other, they are c1t0d0, c1t1d0, andc1t2d0.

80 Understanding Serviceguard Software Components