diff --git a/weed/server/volume_grpc_erasure_coding.go b/weed/server/volume_grpc_erasure_coding.go
index ec868aa9c..32446bf90 100644
--- a/weed/server/volume_grpc_erasure_coding.go
+++ b/weed/server/volume_grpc_erasure_coding.go
@@ -36,6 +36,25 @@ Steps to apply erasure coding to .dat .idx files
 
 */
 
+// isGenerationCompatible checks if requested and actual generations are compatible
+// for mixed-version cluster support
+func isGenerationCompatible(actualGeneration, requestedGeneration uint32) bool {
+	// Exact match is always compatible
+	if actualGeneration == requestedGeneration {
+		return true
+	}
+
+	// Mixed-version compatibility: if client requests generation 0 (default/legacy),
+	// allow access to any generation for backward compatibility
+	if requestedGeneration == 0 {
+		return true
+	}
+
+	// If client requests specific generation but volume has different generation,
+	// this is not compatible (strict generation matching)
+	return false
+}
+
 // VolumeEcShardsGenerate generates the .ecx and .ec00 ~ .ec13 files
 func (vs *VolumeServer) VolumeEcShardsGenerate(ctx context.Context, req *volume_server_pb.VolumeEcShardsGenerateRequest) (*volume_server_pb.VolumeEcShardsGenerateResponse, error) {
 
@@ -370,9 +389,9 @@ func (vs *VolumeServer) VolumeEcShardRead(req *volume_server_pb.VolumeEcShardRea
 		return fmt.Errorf("VolumeEcShardRead not found ec volume id %d", req.VolumeId)
 	}
 
-	// Validate generation matches the request
+	// Validate generation matches with mixed-version compatibility
 	requestedGeneration := req.Generation
-	if ecVolume.Generation != requestedGeneration {
+	if !isGenerationCompatible(ecVolume.Generation, requestedGeneration) {
 		return fmt.Errorf("VolumeEcShardRead volume %d generation mismatch: requested %d, found %d",
 			req.VolumeId, requestedGeneration, ecVolume.Generation)
 	}
diff --git a/weed/storage/store_ec.go b/weed/storage/store_ec.go
index cc79730c3..39da17a80 100644
--- a/weed/storage/store_ec.go
+++ b/weed/storage/store_ec.go
@@ -273,13 +273,23 @@ func (s *Store) cachedLookupEcShardLocations(ecVolume *erasure_coding.EcVolume)
 
 		ecVolume.ShardLocationsLock.Lock()
 		for _, shardIdLocations := range resp.ShardIdLocations {
-			// Validate that the returned generation matches our request
-			if shardIdLocations.Generation != ecVolume.Generation {
+			// Mixed-version compatibility: be more flexible with generation matching
+			// If we requested generation 0 or if the response has generation 0 (older master),
+			// be more permissive to support rolling upgrades
+			generationMatches := shardIdLocations.Generation == ecVolume.Generation
+			mixedVersionCompatible := (ecVolume.Generation == 0 || shardIdLocations.Generation == 0)
+
+			if !generationMatches && !mixedVersionCompatible {
 				glog.Warningf("received shard locations for generation %d but requested generation %d for volume %d shard %d",
 					shardIdLocations.Generation, ecVolume.Generation, ecVolume.VolumeId, shardIdLocations.ShardId)
 				continue // skip mismatched generation shards
 			}
 
+			if !generationMatches && mixedVersionCompatible {
+				glog.V(1).Infof("accepting shard locations with generation mismatch for mixed-version compatibility: volume %d shard %d response_gen=%d requested_gen=%d",
+					ecVolume.VolumeId, shardIdLocations.ShardId, shardIdLocations.Generation, ecVolume.Generation)
+			}
+
 			shardId := erasure_coding.ShardId(shardIdLocations.ShardId)
 			delete(ecVolume.ShardLocations, shardId)
 			for _, loc := range shardIdLocations.Locations {
diff --git a/weed/topology/topology_ec.go b/weed/topology/topology_ec.go
index fa31ebfe4..570c7b062 100644
--- a/weed/topology/topology_ec.go
+++ b/weed/topology/topology_ec.go
@@ -307,35 +307,44 @@ func (t *Topology) ListEcVolumesWithActiveGeneration() map[needle.VolumeId]uint3
 }
 
 // LookupEcShardsWithFallback looks up EC shards for a volume with intelligent fallback
+// This function provides mixed-version cluster compatibility by falling back gracefully
 // If no specific generation is requested (generation == 0), it uses the active generation
 // If the requested/active generation is not found, it falls back to generation 0
 func (t *Topology) LookupEcShardsWithFallback(vid needle.VolumeId, requestedGeneration uint32) (locations *EcShardLocations, actualGeneration uint32, found bool) {
 	// Determine target generation
 	targetGeneration := requestedGeneration
 	if requestedGeneration == 0 {
-		// Use active generation if available
+		// Use active generation if available (new behavior)
 		if activeGen, exists := t.GetEcActiveGeneration(vid); exists {
 			targetGeneration = activeGen
+			glog.V(4).Infof("LookupEcShardsWithFallback: using active generation %d for volume %d", activeGen, vid)
 		}
 	}
 
 	// Try the target generation first
 	if locations, found = t.LookupEcShards(vid, targetGeneration); found {
+		if targetGeneration != requestedGeneration {
+			glog.V(3).Infof("LookupEcShardsWithFallback: found volume %d generation %d (requested %d)", vid, targetGeneration, requestedGeneration)
+		}
 		return locations, targetGeneration, true
 	}
 
-	// If requested specific generation and not found, don't fallback
+	// If requested specific generation and not found, don't fallback for strict clients
 	if requestedGeneration != 0 {
+		glog.V(2).Infof("LookupEcShardsWithFallback: volume %d generation %d not found, no fallback for specific request", vid, requestedGeneration)
 		return nil, 0, false
 	}
 
-	// Fallback to generation 0 if target generation wasn't found
+	// Mixed-version compatibility: fallback to generation 0 if target generation wasn't found
+	// This helps during rolling upgrades when some shards might not have generation info yet
 	if targetGeneration != 0 {
 		if locations, found = t.LookupEcShards(vid, 0); found {
+			glog.V(2).Infof("LookupEcShardsWithFallback: falling back to generation 0 for volume %d (target generation %d not found)", vid, targetGeneration)
 			return locations, 0, true
 		}
 	}
 
+	glog.V(2).Infof("LookupEcShardsWithFallback: volume %d not found in any generation", vid)
 	return nil, 0, false
 }