+ASM1 Fails to Join +ASM2 During Rolling Upgrade from 12c to 19c

Bug 30452852 is a particularly nasty corner case in rolling Grid Infrastructure upgrades: after upgrading node 1 to 19c, the upgraded +ASM1 instance (running 19c) cannot join the cluster because +ASM2 is still running 12c — and the two versions cannot communicate properly in certain network configurations.

Scenario:

Node 1: Grid Infrastructure 19.3.0, +ASM1 — upgraded
Node 2: Grid Infrastructure 12.1.0.2, +ASM2 — still on 12c

During the rolling upgrade window, both ASM instances must briefly coexist. In a properly configured cluster, 19c ASM is backward-compatible with 12c ASM for this transition. Bug 30452852 causes that compatibility to break.

Symptoms:

• +ASM1 crashes immediately after starting, citing I/O errors on voting disks
• Alert log on node 1: GMON: detected ASM instance eviction — cannot reach quorum
• crsctl stat res ora.asm -t shows +ASM1 OFFLINE, +ASM2 ONLINE

Technical cause:

The bug is in the inter-instance GMON (Global Membership Oracle Network) communication protocol. A version mismatch in the GMON handshake message format causes +ASM1 to interpret a valid 12c heartbeat as a corrupted packet and self-evict as a safety measure.

Workaround:

Before starting the upgrade:

# Set this parameter in ASM spfile or init.ora
_asm_compatibility_override = '12.1.0.2'

This tells 19c ASM to use the 12c-compatible message format during the transition. Remove it after both nodes are on 19c.

The fix is available in the 19.8+ patch set. If you’re running 19.3 or 19.5, this parameter workaround is essential for rolling upgrades in multi-node configurations.