fix: admin info output and improve overall performance (#10015)

- admin info node offline check is now quicker
- admin info now doesn't duplicate the code
  across doing the same checks for disks
- rely on StorageInfo to return appropriate errors
  instead of calling locally.
- diskID checks now return proper errors when
  disk not found v/s format.json missing.
- add more disk states for more clarity on the
  underlying disk errors.

cmd/fs-v1.go

@@ -53,9 +53,6 @@ var defaultEtag = "00000000000000000000000000000000-1"
 type FSObjects struct {
 	GatewayUnsupported
 
-	// Disk usage metrics
-	totalUsed uint64 // ref: https://golang.org/pkg/sync/atomic/#pkg-note-BUG
-
 	// The count of concurrent calls on FSObjects API
 	activeIOCount int64
 	// The active IO count ceiling for crawling to work
@@ -215,15 +212,15 @@ func (fs *FSObjects) StorageInfo(ctx context.Context, _ bool) (StorageInfo, []er
 		return StorageInfo{}, []error{err}
 	}
 	used := di.Total - di.Free
-	if !fs.diskMount {
-		used = atomic.LoadUint64(&fs.totalUsed)
-	}
-
 	storageInfo := StorageInfo{
-		Used:       []uint64{used},
-		Total:      []uint64{di.Total},
-		Available:  []uint64{di.Free},
-		MountPaths: []string{fs.fsPath},
+		Disks: []madmin.Disk{
+			{
+				TotalSpace:     di.Total,
+				UsedSpace:      used,
+				AvailableSpace: di.Free,
+				DrivePath:      fs.fsPath,
+			},
+		},
 	}
 	storageInfo.Backend.Type = BackendFS
 	return storageInfo, nil