diff -up btrfs-progs-0.20.rc1.20121017git91d9eec/Makefile.patch4 btrfs-progs-0.20.rc1.20121017git91d9eec/Makefile

--- btrfs-progs-0.20.rc1.20121017git91d9eec/Makefile.patch4	2012-10-04 20:35:31.000000000 -0400

+++ btrfs-progs-0.20.rc1.20121017git91d9eec/Makefile	2012-10-17 13:48:02.331453645 -0400

@@ -67,7 +67,7 @@ btrfsck: $(objects) btrfsck.o

 	$(CC) $(CFLAGS) -o btrfsck btrfsck.o $(objects) $(LDFLAGS) $(LIBS)

 mkfs.btrfs: $(objects) mkfs.o

-	$(CC) $(CFLAGS) -o mkfs.btrfs $(objects) mkfs.o $(LDFLAGS) $(LIBS)

+	$(CC) $(CFLAGS) -o mkfs.btrfs $(objects) mkfs.o $(LDFLAGS) $(LIBS) -lblkid

 btrfs-debug-tree: $(objects) debug-tree.o

 	$(CC) $(CFLAGS) -o btrfs-debug-tree $(objects) debug-tree.o $(LDFLAGS) $(LIBS)

diff -up btrfs-progs-0.20.rc1.20121017git91d9eec/man/mkfs.btrfs.8.in.patch4 btrfs-progs-0.20.rc1.20121017git91d9eec/man/mkfs.btrfs.8.in

--- btrfs-progs-0.20.rc1.20121017git91d9eec/man/mkfs.btrfs.8.in.patch4	2012-10-04 20:35:31.000000000 -0400

+++ btrfs-progs-0.20.rc1.20121017git91d9eec/man/mkfs.btrfs.8.in	2012-10-17 13:48:02.331453645 -0400

@@ -47,7 +47,10 @@ Specify a label for the filesystem.

 .TP

 \fB\-m\fR, \fB\-\-metadata \fIprofile\fR

 Specify how metadata must be spanned across the devices specified. Valid

-values are raid0, raid1, raid10 or single.

+values are raid0, raid1, raid10, single or dup.  Single device will have dup

+set by default except in the case of SSDs which will default to single.  This is

+because SSDs can remap blocks internally so duplicate blocks could end up in the

+same erase block which negates the benefits of doing metadata duplication.

 .TP

 \fB\-M\fR, \fB\-\-mixed\fR

 Mix data and metadata chunks together for more efficient space 

diff -up btrfs-progs-0.20.rc1.20121017git91d9eec/mkfs.c.patch4 btrfs-progs-0.20.rc1.20121017git91d9eec/mkfs.c

--- btrfs-progs-0.20.rc1.20121017git91d9eec/mkfs.c.patch4	2012-10-17 13:48:02.329453660 -0400

+++ btrfs-progs-0.20.rc1.20121017git91d9eec/mkfs.c	2012-10-17 13:53:36.954806793 -0400

@@ -37,6 +37,7 @@

 #include <linux/fs.h>

 #include <ctype.h>

 #include <attr/xattr.h>

+#include <blkid/blkid.h>

 #include "kerncompat.h"

 #include "ctree.h"

 #include "disk-io.h"

@@ -234,7 +235,7 @@ static int create_one_raid_group(struct

 static int create_raid_groups(struct btrfs_trans_handle *trans,

 			      struct btrfs_root *root, u64 data_profile,

 			      int data_profile_opt, u64 metadata_profile,

-			      int metadata_profile_opt, int mixed)

+			      int metadata_profile_opt, int mixed, int ssd)

 {

 	u64 num_devices = btrfs_super_num_devices(&root->fs_info->super_copy);

 	u64 allowed;

@@ -245,8 +246,12 @@ static int create_raid_groups(struct btr

 	 * For mixed groups defaults are single/single.

 	 */

 	if (!metadata_profile_opt && !mixed) {

+		if (num_devices == 1 && ssd)

+			printf("Detected a SSD, turning off metadata "

+			       "duplication.  Mkfs with -m dup if you want to "

+			       "force metadata duplication.\n");

 		metadata_profile = (num_devices > 1) ?

-			BTRFS_BLOCK_GROUP_RAID1 : BTRFS_BLOCK_GROUP_DUP;

+			BTRFS_BLOCK_GROUP_RAID1 : (ssd) ? 0: BTRFS_BLOCK_GROUP_DUP;

 	}

 	if (!data_profile_opt && !mixed) {

 		data_profile = (num_devices > 1) ?

@@ -1215,6 +1220,49 @@ static int check_leaf_or_node_size(u32 s

 	return 0;

 }

+static int is_ssd(const char *file)

+{

+	char *devname;

+	blkid_probe probe;

+	char *dev;

+	char path[PATH_MAX];

+	dev_t disk;

+	int fd;

+	char rotational;

+

+	probe = blkid_new_probe_from_filename(file);

+	if (!probe)

+		return 0;

+

+	/*

+	 * We want to use blkid_devno_to_wholedisk() but it's broken for some

+	 * reason on F17 at least so we'll do this trickery

+	 */

+	disk = blkid_probe_get_wholedisk_devno(probe);

+	devname = blkid_devno_to_devname(disk);

+

+	dev = strrchr(devname, '/');

+	dev++;

+

+	snprintf(path, PATH_MAX, "/sys/block/%s/queue/rotational", dev);

+

+	free(devname);

+	blkid_free_probe(probe);

+

+	fd = open(path, O_RDONLY);

+	if (fd < 0) {

+		return 0;

+	}

+

+	if (read(fd, &rotational, sizeof(char)) < sizeof(char)) {

+		close(fd);

+		return 0;

+	}

+	close(fd);

+

+	return !atoi((const char *)&rotational);

+}

+

 int main(int ac, char **av)

 {

 	char *file;

@@ -1241,6 +1289,7 @@ int main(int ac, char **av)

 	int data_profile_opt = 0;

 	int metadata_profile_opt = 0;

 	int nodiscard = 0;

+	int ssd = 0;

 	char *source_dir = NULL;

 	int source_dir_set = 0;

@@ -1360,6 +1409,9 @@ int main(int ac, char **av)

 			exit(1);

 		}

 	}

+

+	ssd = is_ssd(file);

+

 	if (mixed) {

 		if (metadata_profile != data_profile) {

 			fprintf(stderr, "With mixed block groups data and metadata "

@@ -1445,7 +1497,7 @@ raid_groups:

 	if (!source_dir_set) {

 		ret = create_raid_groups(trans, root, data_profile,

 				 data_profile_opt, metadata_profile,

-				 metadata_profile_opt, mixed);

+				 metadata_profile_opt, mixed, ssd);

 		BUG_ON(ret);

 	}