diff --git a/bcache.h b/bcache.h
index 0054f7d8..3f94dcee 100644
--- a/bcache.h
+++ b/bcache.h
@@ -18,8 +18,11 @@ struct cache_sb {
 	uint64_t	nbuckets;	/* device size */
 	uint64_t	btree_root;
 	uint16_t	btree_level;
-	uint16_t	_pad[3];
+	uint16_t	nr_in_set;
+	uint16_t	nr_this_dev;
+	uint16_t	_pad[1];
 	uint8_t		uuid[16];
+	uint8_t		set_uuid[16];
 };
 
 struct bucket_disk {
diff --git a/make-bcache.c b/make-bcache.c
index adc90ac9..b213f9e4 100644
--- a/make-bcache.c
+++ b/make-bcache.c
@@ -76,6 +76,7 @@ int main(int argc, char **argv)
 	struct cache_sb sb = { .block_size = 8, .bucket_size = 0 };
 
 	uuid_generate(sb.uuid);
+	uuid_generate(sb.set_uuid);
 
 	while ((c = getopt(argc, argv, "CBU:w:b:")) != -1)
 		switch (c) {
@@ -129,6 +130,7 @@ int main(int argc, char **argv)
 	memcpy(sb.magic, bcache_magic, 16);
 	sb.version = backingdev ? CACHE_BACKING_DEVICE : 0;
 	sb.nbuckets = nblocks / sb.bucket_size;
+	sb.nr_in_set = 1;
 	uuid_unparse(sb.uuid, uuid);
 
 	do