--- volumes.c.orig	2012-01-20 16:59:31.000000000 +0100
+++ volumes.c	2012-01-24 11:24:07.261401805 +0100
@@ -2329,6 +2329,8 @@
 	u64 stripe_size;
 	u64 num_bytes;
 	int ndevs;
+	u64 fs_total_avail;
+	int opt_ndevs;
 	int i;
 	int j;
 
@@ -2448,6 +2450,7 @@
 		devices_info[ndevs].total_avail = total_avail;
 		devices_info[ndevs].dev = device;
 		++ndevs;
+		fs_total_avail += total_avail;
 	}
 
 	/*
@@ -2456,6 +2459,16 @@
 	sort(devices_info, ndevs, sizeof(struct btrfs_device_info),
 	     btrfs_cmp_device_info, NULL);
 
+	/*
+	* do not allocate space on all devices
+	* instead balance free space to maximise space utilization
+	*/
+	opt_ndevs = (fs_total_avail*2 + devs_increment*devices_info[0].total_avail)/(devices_info[0].total_avail*2);
+	if (opt_ndevs < devs_min)
+		opt_ndevs = devs_min;
+	if (ndevs > opt_ndevs)
+		ndevs = opt_ndevs;
+
 	/* round down to number of usable stripes */
 	ndevs -= ndevs % devs_increment;