--- vdev_geom.c.ori	2010-12-05 15:08:09.000000000 +0100
+++ vdev_geom.c	2010-12-05 15:10:50.000000000 +0100
@@ -496,7 +496,10 @@
 	/*
 	 * Determine the device's minimum transfer size.
 	 */
-	*ashift = highbit(MAX(pp->sectorsize, SPA_MINBLOCKSIZE)) - 1;
+	if (pp->stripesize != 0 && pp->stripesize > pp->sectorsize)
+		*ashift = highbit(MIN(pp->stripesize, SPA_MAXBLOCKSIZE)) - 1;
+	else
+		*ashift = highbit(MAX(pp->sectorsize, SPA_MINBLOCKSIZE)) - 1;
 
 	/*
 	 * Clear the nowritecache bit, so that on a vdev_reopen() we will