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VERITAS Volume Manager 3.1 Administrator's Guide: for HP-UX 11i and HP-UX 11i Version 1.5 > Chapter 3 Volume Manager Operations
Volume Manager Rootability |
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Rootability is the term used to indicate that the logical volumes containing the root file system and the system swap area are under Volume Manager control. Normally the Volume Manager is started following a successful boot after the operating system has passed control to the initial user mode process. However, when the volume containing the root file system is under Volume Manager control, portions of the Volume Manager must be started early from the operating system kernel before the operating system starts the first user process. Thus, the Volume Manager code that enables rootability is contained within the operating system kernel. An HP-UX boot disk is set up to contain a Logical Interchchange format (LIF) area. Part of the LIF structure is a LIF LABEL record, which contains information about the starting block number and length of the volumes containing the stand and root filesystems as well as the volume containing the system swap area. Part of the procedure for making a disk VxVM-rootable is to initialize the LIF LABEL record with volume extent information for the stand, root, swap, and, optionally, dump volumes. This is done with vxbootsetup(1M). Before the kernel mounts the root file system, it determines if the boot disk was a rootable VxVM disk. If so, then the kernel passes control to the kernel Volume Manager rootability code. The kernel rootability code extracts the starting block number and length of the root and swap volumes from the LIF LABEL record and builds “fake” volume and disk configuration objects for these volumes and then loads this fake configuration into the VxVM kernel driver. At this point, I/O can proceed on these fake root and swap volumes by simply referencing the device number that was set up by the rootability code. Once the kernel passes control to the initial user procedure (pre_init_rc()), the Volume Manager daemon starts and reads the configuration of the volumes in the root disk group and loads them into the kernel. At this time the fake root and swap volume hierarchy can be discarded, as further I/O to these volumes will be done through the normal configuration objects just loaded into the kernel. The volumes that need to be available at boot time have some very specific restrictions on their configuration. These restrictions include their names, the disk group they are in, their volume usage types, and they must be single subdisk, contiguous volumes. These restrictions are detailed below:
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