Using VxVM Maintenance Mode Boot (MMB)
Another method for performing limited recovery on a VxVM boot disk is to use the VxVM Maintenance Mode Boot (MMB). MMB mode is initiated by booting the system and gaining control at the ISL prompt. Boot the system from the primary or secondary boot device, and enter the following command at the boot prompt:
hpux -vm
This causes the bootloader and the HP-UX kernel to take alternate actions in finding the parts of the system that are required to boot the system.
The bootloader starts reading the stand file system at 1KB block 3168 instead of locating it from the LIF label. The VxVM kernel rootability code uses root volume extent information in the /stand/rootconf file to set up the extents of the root volume, and init is instructed to bring the system up to single-user mode. When invoked from the pre_init_rc script, the vxconfigd daemon exits gracefully if it determines from the kernel that the system is in MMB mode. The system is left running with only the root volume mounted, and VxVM runs with temporary objects pointing to the root volume.
 Caution
The VxVM configuration daemon, vxconfigd, does not normally run in MMB mode, and only one copy of the root volume data is used. If the system has a mirrored root volume, writing to the root file system can thus cause file system corruption when both mirrors are subsequently configured. To prevent this, start VxVM in MMB mode by running the vx_emerg_start command. This marks the non-boot mirror plexes as stale, and so forces a recovery from the boot mirror to the non-boot mirrors to take place. After VxVM has been started in MMB mode, various recovery options can be performed depending on the nature of the problem. For more information, see the vx_emerg_start(1M) manual page.
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