diff --git a/sys/fs/udf/udf.h b/sys/fs/udf/udf.h
index bce91861e1a5..28289a205802 100644
--- a/sys/fs/udf/udf.h
+++ b/sys/fs/udf/udf.h
@@ -1,4 +1,4 @@
-/* $NetBSD: udf.h,v 1.18 2008/07/17 19:10:22 reinoud Exp $ */
+/* $NetBSD: udf.h,v 1.19 2008/07/19 16:00:35 reinoud Exp $ */
 
 /*
  * Copyright (c) 2006, 2008 Reinoud Zandijk
@@ -179,6 +179,11 @@ extern int udf_verbose;
 #define UDF_ALLOC_RELAXEDSEQUENTIAL  6  /* only nodes not seq.           */
 
 
+/* allocation descriptor styles */
+#define UDF_ALLOCDSCR_SHORT	     1	/* use short_ad allocation dscr. */
+#define UDF_ALLOCDSCR_LONG	     2	/* use long_ad  allocation dscr. */
+
+
 /* logical volume open/close actions */
 #define UDF_OPEN_SESSION	  0x01  /* if needed writeout VRS + VDS	     */
 #define UDF_CLOSE_SESSION	  0x02	/* close session after writing VAT   */
@@ -283,9 +288,11 @@ struct udf_mount {
 	int			 lvclose;		/* logvol actions    */
 
 	/* disc allocation / writing method */
-	int			 lvreadwrite;		/* bits */
-	int			 data_alloc;		/* all userdata */
-	int			 meta_alloc;		/* all metadata */
+	int			 lvreadwrite;		/* error handling    */
+	int			 data_alloc;		/* all userdata      */
+	int			 data_allocdscr;
+	int			 meta_alloc;		/* all metadata      */
+	int			 meta_allocdscr;
 	int			 data_part;
 	int			 metadata_part;
 	kmutex_t		 allocate_mutex;
diff --git a/sys/fs/udf/udf_subr.c b/sys/fs/udf/udf_subr.c
index 539ab6ae5c1c..24efc804a5a6 100644
--- a/sys/fs/udf/udf_subr.c
+++ b/sys/fs/udf/udf_subr.c
@@ -1,4 +1,4 @@
-/* $NetBSD: udf_subr.c,v 1.63 2008/07/18 15:55:32 reinoud Exp $ */
+/* $NetBSD: udf_subr.c,v 1.64 2008/07/19 16:00:35 reinoud Exp $ */
 
 /*
  * Copyright (c) 2006, 2008 Reinoud Zandijk
@@ -29,7 +29,7 @@
 
 #include <sys/cdefs.h>
 #ifndef lint
-__KERNEL_RCSID(0, "$NetBSD: udf_subr.c,v 1.63 2008/07/18 15:55:32 reinoud Exp $");
+__KERNEL_RCSID(0, "$NetBSD: udf_subr.c,v 1.64 2008/07/19 16:00:35 reinoud Exp $");
 #endif /* not lint */
 
 
@@ -1815,6 +1815,17 @@ udf_process_vds(struct udf_mount *ump) {
 		}
 	}
 
+	/* determine default allocation descriptors to use */
+	ump->data_allocdscr = UDF_ALLOCDSCR_SHORT;
+	ump->meta_allocdscr = UDF_ALLOCDSCR_SHORT;
+	if (n_pm > 1) {
+		ump->data_allocdscr = UDF_ALLOCDSCR_LONG;
+		ump->meta_allocdscr = UDF_ALLOCDSCR_LONG;
+		/* metadata partitions are forced to have short */
+		if (n_meta)
+			ump->meta_allocdscr = UDF_ALLOCDSCR_SHORT;
+	}
+
 	/* determine logical volume open/closure actions */
 	if (n_virt) {
 		ump->lvopen  = 0;