VERITAS Volume Manager 3.5 Troubleshooting Guide (September 2004)
Recovery from Boot Disk Failure
Using VxVM Maintenance Mode Boot (MMB)
Chapter 2
35
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 Use extreme caution when attempting to bring a system up in MMB mode if the system
has a mirrored root volume. The vxconfigd daemon does not run in this mode, and only
one copy of the root volume data is used. Writing to the root file system in MMB mode
can cause file system corruption when both mirrors are subsequently configured.
Use the vx_emerg_start command to start the volume manager while in MMB mode.
This command avoids writing to the root file system when the system is in MMB mode
unless it needs to update the volboot file.
If it is necessary to update the volboot file in MMB mode, the vx_emerg_start
command warns you that you must re-run vx_emerg_start with the -f (force) option
specified to perform the write.
After running vx_emerg_start to start VxVM while in MMB mode on a mirrored root, it
is recommended that you remove the half of the mirror from which the system was not
booted. This can be done as follows:
Step 1. Determine which disk you booted from.
Step 2. Run the command vxdisk list, and locate your system’s boot disk in the leftmost
DEVICE column of the output. Find the disk media (DM) name of the boot device by
locating the boot device in the DISK column. The name of this device should be similar to
rootdisk01 or rootdisk02. Also note the disk media name of the mirror disk.
Step 3. Run the following command:
# vxprint -g rootdg rootvol
If your system has a mirrored root volume, two plex entry lines are listed (with pl in the
leftmost column), and immediately below each plex entry is the subdisk entry that is
associated with the plex (with sd in the leftmost column).
Step 4. Examine the NAME field that is immediately to the right of the sd entry. This is the
subdisk name, which is composed of the DM name followed by
-nn
, where
nn
is a number,
such as 03 or 04, that uniquely identifies the subdisk. Identify the disk media name of
the root mirror disk from which the system was not booted.