When
multiple nodes boot from a common system disk shadow set, ensure
that all nodes specify a physical disk that is a source member of
the system disk shadow set.
At boot time, the volume shadowing software attempts to construct
a complete system disk shadow set based on the shadowing membership
information contained in the storage control block (SCB) of
the boot device. The
SCB is an ODS-2 or ODS-5 file system data structure that resides
on each storage device and contains information about shadow set
membership (described in
Shadow Set Consistency). Depending on what information is in the
SCB at boot time, the following scenarios are possible:
If the boot device was not formerly
a member of a shadow set, the system creates a new shadow set containing
only the boot device. You can manually mount additional disks into
the shadow set after the system boot procedure completes. (See the
Caution that follows.)
If the boot device is already a valid member of
an existing shadow set (for instance, if it is already an up-to-date
member of a shadow set mounted by another node in the cluster),
the shadowing software automatically locates all the members of
the set.
When booting the first node in a cluster, information
stored in the SCB of the physical boot device is used to locate
other members of the shadow set and to create the complete system
disk shadow set.
The shadowing software detects boot attempts from
a physical disk that is inconsistent with currently active shadow
set members. In this case, the boot attempt detects the existence
of the other shadow set members and determines (using the information
in the SCB) that the boot device is not a valid member of the shadow
set. When this occurs, the boot attempt fails with a SHADBOOTFAIL
bugcheck message on the system console, and a dump file is written
to the boot device. The system bugchecks because it can boot only from a currently
valid member of the system disk shadow set. If the boot device fails
out of or is otherwise removed from the system disk shadow set,
you must either mount the boot device back into the shadow set (and
wait for the copy operation to complete) or modify the boot command
file to boot from a current shadow set member.
The boot process automatically locates all the members of
a system disk shadow set. You should not add system disk shadow
set members in startup procedures as formerly recommended when phase
I shadowing was supported.
Do not add members to a system disk
shadow set in startup procedures. Doing so can result in loss of
data under the following circumstances:
A system
is operating normally with a multiple member system disk shadow
set.
The original boot device is removed from the shadow
set but remains as a functioning disk.
The system continues with the remaining members.
The system is shut down or it fails.
The system is rebooted using the original boot device
(which is now out of date).
The boot process determines that the boot device
is not consistent with the other shadow set members and, therefore,
does not add them into the shadow set. This behavior preserves the
up-to-date data on the other members.
A MOUNT command in the startup procedure adds the
other shadow set members to the system disk shadow set.
A copy operation from the boot device to the other
shadow set members is initiated, thereby overwriting them.
If the boot device fails, the following console warning message
displays:
virtual-unit: does not contain the member named to VMB.
System may not reboot.
After the boot device has been repaired, manually add it back
into the system disk shadow set.