The following UNXSIGNAL bug check is a historical field observation from OpenVMS Alpha V6.2 when an application first allocated space on a newly mounted virtual disk. It has not been reproduced as part of Avanti 5.1.0 qualification and must not be read as applying to every OpenVMS release before V7.3.

**** OpenVMS (TM) Alpha Operating System V6.2     - BUGCHECK ****
** Code=0000041C: UNXSIGNAL, Unexpected signal name in ACP
** Crash CPU: 00    Primary CPU: 00    Active CPUs: 00000001
** Current Process = BPCD_BG30
** Image Name = BUILD$DKC0:[OPENV.NETBACKUP]BPCD_AXP.EXE;1

This crash is due to an old disk geometry problem.  The problem causes an overflow in one of the following UCB fields:

UCB$B_SECTORS
UCB$B_TRACKS
UCB$W_CYLINDERS  

This results in the VCB$L_BLOCKFACT field in the VCB being zero.  The first space allocation on the volume generates a divide-by-zero error, which crashes the system with a UNXSIGNAL bugcheck.

Historical guidance identifies a MOUNTSHR.EXE correction in OpenVMS V7.3 and the patch kits listed below. These package names and their applicability have not been independently verified against a current vendor patch catalog; confirm the correct kit for the exact guest release before installation.

Historically referenced patch kits:

MOUNTSHR.EXE_V62R
VMOUNT.EXE_V62R
VMS73_F11X-V0200
VMS73_F11X-V0300

As a historical workaround, field guidance used changing the virtual-disk size; for example, an affected RZ25 configuration was changed to an RZ56. This workaround has not been reproduced for Avanti 5.1.0. Verify it against the exact guest release and preserve the original disk configuration before applying it.