diff --git a/header/src/main/java/org/zstack/header/storage/ceph/CephSiblingFenceExtensionPoint.java b/header/src/main/java/org/zstack/header/storage/ceph/CephSiblingFenceExtensionPoint.java
new file mode 100644
index 00000000000..a9a4ed54550
--- /dev/null
+++ b/header/src/main/java/org/zstack/header/storage/ceph/CephSiblingFenceExtensionPoint.java
@@ -0,0 +1,18 @@
+package org.zstack.header.storage.ceph;
+
+import org.zstack.header.core.ReturnValueCompletion;
+
+/**
+ * SPI for Ceph HA sibling-fence (ZSTAC-83890).
+ * Implementation lives in premium {@code storage-ha-plugin}.
+ * Called from {@code CephPrimaryStorageFactory.preInstantiateVmResource} when
+ * Ceph watcher list is empty — SSH-kills stale QEMU on the failed host before
+ * HA starts the VM to prevent split-brain.
+ */
+public interface CephSiblingFenceExtensionPoint {
+    void fenceVmOnFailedHost(String failedHostUuid,
+                             String vmUuid,
+                             String clusterUuid,
+                             String haTargetHostUuid,
+                             ReturnValueCompletion<SiblingFenceVmOnHostReply> completion);
+}
diff --git a/header/src/main/java/org/zstack/header/storage/ceph/SiblingFenceVmOnHostMsg.java b/header/src/main/java/org/zstack/header/storage/ceph/SiblingFenceVmOnHostMsg.java
new file mode 100644
index 00000000000..a3bfad147cc
--- /dev/null
+++ b/header/src/main/java/org/zstack/header/storage/ceph/SiblingFenceVmOnHostMsg.java
@@ -0,0 +1,42 @@
+package org.zstack.header.storage.ceph;
+
+import org.zstack.header.message.NeedReplyMessage;
+
+public class SiblingFenceVmOnHostMsg extends NeedReplyMessage {
+    private String failedHostUuid;
+    private String vmUuid;
+    private String clusterUuid;
+    private String haTargetHostUuid;
+
+    public String getFailedHostUuid() {
+        return failedHostUuid;
+    }
+
+    public void setFailedHostUuid(String failedHostUuid) {
+        this.failedHostUuid = failedHostUuid;
+    }
+
+    public String getVmUuid() {
+        return vmUuid;
+    }
+
+    public void setVmUuid(String vmUuid) {
+        this.vmUuid = vmUuid;
+    }
+
+    public String getClusterUuid() {
+        return clusterUuid;
+    }
+
+    public void setClusterUuid(String clusterUuid) {
+        this.clusterUuid = clusterUuid;
+    }
+
+    public String getHaTargetHostUuid() {
+        return haTargetHostUuid;
+    }
+
+    public void setHaTargetHostUuid(String haTargetHostUuid) {
+        this.haTargetHostUuid = haTargetHostUuid;
+    }
+}
diff --git a/header/src/main/java/org/zstack/header/storage/ceph/SiblingFenceVmOnHostReply.java b/header/src/main/java/org/zstack/header/storage/ceph/SiblingFenceVmOnHostReply.java
new file mode 100644
index 00000000000..400297f8f6b
--- /dev/null
+++ b/header/src/main/java/org/zstack/header/storage/ceph/SiblingFenceVmOnHostReply.java
@@ -0,0 +1,69 @@
+package org.zstack.header.storage.ceph;
+
+import org.zstack.header.message.MessageReply;
+
+public class SiblingFenceVmOnHostReply extends MessageReply {
+    private boolean alive;
+    private boolean killed;
+    private boolean sshReachable;
+    private boolean qemuFound;
+    private String executorHostUuid;
+    private String executorRole;
+    private String reason;
+
+    public boolean isAlive() {
+        return alive;
+    }
+
+    public void setAlive(boolean alive) {
+        this.alive = alive;
+    }
+
+    public boolean isKilled() {
+        return killed;
+    }
+
+    public void setKilled(boolean killed) {
+        this.killed = killed;
+    }
+
+    public boolean isSshReachable() {
+        return sshReachable;
+    }
+
+    public void setSshReachable(boolean sshReachable) {
+        this.sshReachable = sshReachable;
+    }
+
+    public boolean isQemuFound() {
+        return qemuFound;
+    }
+
+    public void setQemuFound(boolean qemuFound) {
+        this.qemuFound = qemuFound;
+    }
+
+    public String getExecutorHostUuid() {
+        return executorHostUuid;
+    }
+
+    public void setExecutorHostUuid(String executorHostUuid) {
+        this.executorHostUuid = executorHostUuid;
+    }
+
+    public String getExecutorRole() {
+        return executorRole;
+    }
+
+    public void setExecutorRole(String executorRole) {
+        this.executorRole = executorRole;
+    }
+
+    public String getReason() {
+        return reason;
+    }
+
+    public void setReason(String reason) {
+        this.reason = reason;
+    }
+}
diff --git a/plugin/ceph/src/main/java/org/zstack/storage/ceph/primary/CephPrimaryStorageFactory.java b/plugin/ceph/src/main/java/org/zstack/storage/ceph/primary/CephPrimaryStorageFactory.java
index cb7dde9c5cc..2c6cc8b71e2 100755
--- a/plugin/ceph/src/main/java/org/zstack/storage/ceph/primary/CephPrimaryStorageFactory.java
+++ b/plugin/ceph/src/main/java/org/zstack/storage/ceph/primary/CephPrimaryStorageFactory.java
@@ -34,6 +34,7 @@
 import org.zstack.header.configuration.userconfig.InstanceOfferingUserConfig;
 import org.zstack.header.configuration.userconfig.InstanceOfferingUserConfigValidator;
 import org.zstack.header.core.Completion;
+import org.zstack.header.core.ReturnValueCompletion;
 import org.zstack.header.core.WhileDoneCompletion;
 import org.zstack.header.core.progress.TaskProgressRange;
 import org.zstack.header.core.workflow.*;
@@ -47,6 +48,8 @@
 import org.zstack.header.host.HostVO_;
 import org.zstack.header.message.MessageReply;
 import org.zstack.header.storage.backup.*;
+import org.zstack.header.storage.ceph.CephSiblingFenceExtensionPoint;
+import org.zstack.header.storage.ceph.SiblingFenceVmOnHostReply;
 import org.zstack.header.storage.primary.*;
 import org.zstack.header.storage.snapshot.*;
 import org.zstack.header.vm.*;
@@ -1229,7 +1232,50 @@ public void run(MessageReply reply) {
                 GetVolumeWatchersReply rly = (GetVolumeWatchersReply)reply;
                 List watchers = rly.getWatchers();
                 if (watchers == null || watchers.isEmpty()) {
-                    completion.success();
+                    List<CephSiblingFenceExtensionPoint> exts =
+                            pluginRgty.getExtensionList(CephSiblingFenceExtensionPoint.class);
+                    if (exts.isEmpty()) {
+                        // Open-source / no premium installed -> preserve original behaviour
+                        completion.success();
+                        return;
+                    }
+
+                    final String vmUuid          = spec.getVmInventory().getUuid();
+                    final String haTargetHostUuid = spec.getDestHost().getUuid();
+                    final String clusterUuid     = spec.getDestHost().getClusterUuid();
+                    final String failedHostUuid  = spec.getVmInventory().getLastHostUuid() != null
+                                                   ? spec.getVmInventory().getLastHostUuid()
+                                                   : spec.getVmInventory().getHostUuid();
+                    if (failedHostUuid == null) {
+                        // No previous host -> fresh instantiation, no fence needed
+                        completion.success();
+                        return;
+                    }
+
+                    CephSiblingFenceExtensionPoint ext = exts.get(0);
+                    logger.debug(String.format("dispatching ceph sibling-fence for vm[%s] on failedHost[%s], target[%s]",
+                            vmUuid, failedHostUuid, haTargetHostUuid));
+                    ext.fenceVmOnFailedHost(failedHostUuid, vmUuid, clusterUuid, haTargetHostUuid,
+                            new ReturnValueCompletion<SiblingFenceVmOnHostReply>(completion) {
+                        @Override
+                        public void success(SiblingFenceVmOnHostReply r) {
+                            if (!r.isAlive() || r.isKilled()) {
+                                logger.debug(String.format("ceph sibling-fence succeeded for vm[%s] on failedHost[%s]: killed=%s sshReachable=%s",
+                                        vmUuid, failedHostUuid, r.isKilled(), r.isSshReachable()));
+                                completion.success();
+                            } else {
+                                logger.warn(String.format("ceph sibling-fence failed for vm[%s] on failedHost[%s]: %s — blocking VM start to prevent split-brain",
+                                        vmUuid, failedHostUuid, r.getReason()));
+                                completion.fail(operr("sibling fence failed: %s", r.getReason()));
+                            }
+                        }
+                        @Override
+                        public void fail(ErrorCode err) {
+                            logger.warn(String.format("ceph sibling-fence error for vm[%s] on failedHost[%s]: %s",
+                                    vmUuid, failedHostUuid, err));
+                            completion.fail(err);
+                        }
+                    });
                     return;
                 }