update comment

Signed-off-by: Steve Kriss <krisss@vmware.com>

pkg/backup/backup.go

@@ -212,8 +212,10 @@ type VolumeSnapshotterGetter interface {
 }
 
 // Backup backs up the items specified in the Backup, placing them in a gzip-compressed tar file
-// written to backupFile. The finalized api.Backup is written to metadata. Any error returned by
-// this function causes the backup to be Failed.
+// written to backupFile. The finalized api.Backup is written to metadata. Any error that represents
+// a complete backup failure is returned. Errors that constitute partial failures (i.e. failures to
+// back up individual resources that don't prevent the backup from continuing to be processed) are logged
+// to the backup log.
 func (kb *kubernetesBackupper) Backup(log logrus.FieldLogger, backupRequest *Request, backupFile io.Writer, actions []velero.BackupItemAction, volumeSnapshotterGetter VolumeSnapshotterGetter) error {
 	gzippedData := gzip.NewWriter(backupFile)
 	defer gzippedData.Close()