feat: add Prometheus metric for volume creation operations (#10026)

* feat: add Prometheus metric for volume creation operations

Add VolumeServerVolumeCreationCounter metric to track volume creation
attempts by result (success/failure).

Changes:
- Add VolumeServerVolumeCreationCounter in weed/stats/metrics.go
- Instrument GrowByCountAndType in weed/topology/volume_growth.go
- Add unit tests in weed/stats/metrics_volume_creation_test.go
- Add Grafana dashboard panel for volume creation rate

This metric enables monitoring volume creation success/failure rates
in SeaweedFS clusters.

* fix: address CodeRabbit review - move failure counter before early return

- Move failure counter into loop else block before return statement
- Move success counter to after loop completion
- Strengthen test assertion from count < 1 to count != 2
- Add t.Cleanup() for test isolation in TestVolumeCreationCounterIncrement

* fix: count each volume create attempt and move metric to master subsystem

- topology runs on the master, so move volume_creation_total from the
  volumeServer subsystem to master (SeaweedFS_master_volume_creation_total);
  rename the var to MasterVolumeCreationCounter and group it with the other
  master metrics.
- increment the counter per findAndGrow iteration instead of once per
  GrowByCountAndType call: each logical volume is now counted, partial
  successes before a failure are credited, and a targetCount==0 call no
  longer records a spurious success.
- update the Grafana panel query and the unit tests; the registration test
  now asserts via the shared Gather registry under the fully-qualified name.

* test: drop volume_creation metric tests

They only exercised the Prometheus client library (CounterVec increment and
registry collection), not any SeaweedFS behavior, so they carried maintenance
cost without verifying anything in this codebase.

---------

Co-authored-by: Ubuntu User <ubuntu@example.com>
Co-authored-by: Chris Lu <chris.lu@gmail.com>

other/metrics/grafana_seaweedfs.json

@@ -4266,6 +4266,102 @@
             }
           ],
           "pluginVersion": "10.3.1"
+        },
+        {
+          "datasource": {
+            "type": "prometheus",
+            "uid": "${DS_PROMETHEUS}"
+          },
+          "title": "Volume Creation Rate",
+          "description": "Rate of volume creation operations by result",
+          "type": "timeseries",
+          "id": 216,
+          "gridPos": {
+            "h": 8,
+            "w": 12,
+            "x": 0,
+            "y": 118
+          },
+          "fieldConfig": {
+            "defaults": {
+              "color": {
+                "mode": "palette-classic"
+              },
+              "custom": {
+                "axisBorderShow": false,
+                "axisCenteredZero": false,
+                "axisColorMode": "text",
+                "axisLabel": "",
+                "axisPlacement": "auto",
+                "barAlignment": 0,
+                "drawStyle": "line",
+                "fillOpacity": 10,
+                "gradientMode": "none",
+                "hideFrom": {
+                  "legend": false,
+                  "tooltip": false,
+                  "viz": false
+                },
+                "insertNulls": false,
+                "lineInterpolation": "linear",
+                "lineWidth": 1,
+                "pointSize": 4,
+                "scaleDistribution": {
+                  "type": "linear"
+                },
+                "showPoints": "never",
+                "spanNulls": false,
+                "stacking": {
+                  "group": "A",
+                  "mode": "none"
+                },
+                "thresholdsStyle": {
+                  "mode": "off"
+                }
+              },
+              "mappings": [],
+              "unit": "ops",
+              "thresholds": {
+                "mode": "absolute",
+                "steps": [
+                  {
+                    "color": "green",
+                    "value": null
+                  }
+                ]
+              }
+            },
+            "overrides": []
+          },
+          "options": {
+            "legend": {
+              "calcs": [
+                "lastNotNull",
+                "max"
+              ],
+              "displayMode": "table",
+              "placement": "bottom",
+              "showLegend": true
+            },
+            "tooltip": {
+              "mode": "multi",
+              "sort": "desc"
+            }
+          },
+          "targets": [
+            {
+              "datasource": {
+                "type": "prometheus",
+                "uid": "${DS_PROMETHEUS}"
+              },
+              "editorMode": "code",
+              "expr": "rate(SeaweedFS_master_volume_creation_total{cluster=~\"$cluster\"}[5m])",
+              "range": true,
+              "refId": "A",
+              "legendFormat": "{{result}}"
+            }
+          ],
+          "pluginVersion": "10.3.1"
         }
       ]
     },

weed/stats/metrics.go

@@ -128,6 +128,16 @@ var (
 			Help:      "Current number of volumes that do not have enough replicas per collection/layout. 0 = healthy.",
 		}, []string{"collection", "disk", "rp", "ttl"})
 
+	// MasterVolumeCreationCounter counts volume creation (growth) operations by result (success, failure).
+	// Volume growth is orchestrated by the master, so this metric is exported by the master process.
+	MasterVolumeCreationCounter = prometheus.NewCounterVec(
+		prometheus.CounterOpts{
+			Namespace: Namespace,
+			Subsystem: "master",
+			Name:      "volume_creation_total",
+			Help:      "Counter of volume creation operations by result (success, failure).",
+		}, []string{"result"})
+
 	MasterPickForWriteErrorCounter = prometheus.NewCounter(
 		prometheus.CounterOpts{
 			Namespace: Namespace,
@@ -863,6 +873,7 @@ func init() {
 	Gather.MustRegister(VolumeServerReplicationTargets)
 	Gather.MustRegister(VolumeServerReplicationFailures)
 	Gather.MustRegister(MasterUnderReplicatedVolumes)
+	Gather.MustRegister(MasterVolumeCreationCounter)
 
 	Gather.MustRegister(S3RequestCounter)
 	Gather.MustRegister(S3HandlerCounter)

weed/topology/volume_growth.go

@@ -13,6 +13,7 @@ import (
 	"google.golang.org/grpc"
 
 	"github.com/seaweedfs/seaweedfs/weed/glog"
+	"github.com/seaweedfs/seaweedfs/weed/stats"
 	"github.com/seaweedfs/seaweedfs/weed/storage"
 	"github.com/seaweedfs/seaweedfs/weed/storage/needle"
 	"github.com/seaweedfs/seaweedfs/weed/storage/super_block"
@@ -136,8 +137,10 @@ func (vg *VolumeGrowth) GrowByCountAndType(grpcDialOption grpc.DialOption, targe
 	for i := uint32(0); i < targetCount; i++ {
 		if res, e := vg.findAndGrow(grpcDialOption, topo, option); e == nil {
 			result = append(result, res...)
+			stats.MasterVolumeCreationCounter.WithLabelValues("success").Inc()
 		} else {
 			glog.V(0).Infof("create %d volume, created %d: %v", targetCount, len(result), e)
+			stats.MasterVolumeCreationCounter.WithLabelValues("failure").Inc()
 			return result, e
 		}
 	}