NIO storage: the nio: prefix was using memory mapped files instead of FileChannel.

h2/src/main/org/h2/store/fs/FileSystemDisk.java

@@ -394,8 +394,7 @@ public class FileSystemDisk extends FileSystem {
             try {
                 f = new FileObjectDisk(fileName, mode);
             } catch (IOException e2) {
-                e2.initCause(e);
-                throw e2;
+                throw e;
             }
         }
         return f;

h2/src/main/org/h2/store/fs/FileSystemDiskNio.java

@@ -68,10 +68,9 @@ public class FileSystemDiskNio extends FileSystemDisk {
         } catch (IOException e) {
             freeMemoryAndFinalize();
             try {
-                f = new FileObjectDiskMapped(fileName, mode);
+                f = open(fileName, mode);
             } catch (IOException e2) {
-                e2.initCause(e);
-                throw e2;
+                throw e;
             }
         }
         return f;