Index: sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_label.c
===================================================================
RCS file: /zoo/cvsup/FreeBSD-CVS/src/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_label.c,v
retrieving revision 1.3
diff -u -p -r1.3 vdev_label.c
--- sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_label.c	17 Nov 2008 20:49:29 -0000	1.3
+++ sys/cddl/contrib/opensolaris/uts/common/fs/zfs/vdev_label.c	20 Aug 2009 08:57:18 -0000
@@ -142,6 +142,7 @@
 #include <sys/metaslab.h>
 #include <sys/zio.h>
 #include <sys/fs/zfs.h>
+#include <sys/sysctl.h>
 
 /*
  * Basic routines to read and write from a vdev label.
@@ -714,9 +715,15 @@ vdev_label_init(vdev_t *vd, uint64_t crt
  * conflicting uberblocks on disk with the same txg.  The solution is simple:
  * among uberblocks with equal txg, choose the one with the latest timestamp.
  */
+SYSCTL_DECL(_vfs_zfs);
+static int maxtxg = -1;
+SYSCTL_INT(_vfs_zfs, OID_AUTO, maxtxg, CTLFLAG_RW, &maxtxg, 0, "");
 static int
 vdev_uberblock_compare(uberblock_t *ub1, uberblock_t *ub2)
 {
+	if (maxtxg != -1 && ub1->ub_txg > (uint64_t)maxtxg)
+		return (-1);
+
 	if (ub1->ub_txg < ub2->ub_txg)
 		return (-1);
 	if (ub1->ub_txg > ub2->ub_txg)