diff --git a/c_src/cmd_option.c b/c_src/cmd_option.c
index 6ce34016f..866dfeb24 100644
--- a/c_src/cmd_option.c
+++ b/c_src/cmd_option.c
@@ -36,16 +36,28 @@ static void set_option_usage(void)
 	exit(EXIT_SUCCESS);
 }
 
+static int name_to_dev_idx(struct bch_fs *c, const char *dev)
+{
+	int ret = -1;
+
+	rcu_read_lock();
+	for_each_member_device_rcu(c, ca, NULL)
+		if (!strcmp(ca->name, dev)) {
+			ret = ca->dev_idx;
+			break;
+		}
+	rcu_read_unlock();
+
+	return ret;
+}
+
 int cmd_set_option(int argc, char *argv[])
 {
-	struct bch_opt_strs new_opt_strs = bch2_cmdline_opts_get(&argc, argv, OPT_MOUNT);
+	struct bch_opt_strs new_opt_strs = bch2_cmdline_opts_get(&argc, argv, OPT_MOUNT|OPT_DEVICE);
 	struct bch_opts new_opts = bch2_parse_opts(new_opt_strs);
-	struct bch_opts open_opts = bch2_opts_empty();
 	unsigned i;
 	int opt, ret = 0;
 
-	opt_set(open_opts, nostart, true);
-
 	while ((opt = getopt(argc, argv, "h")) != -1)
 		switch (opt) {
 		case 'h':
@@ -59,48 +71,102 @@ int cmd_set_option(int argc, char *argv[])
 		exit(EXIT_FAILURE);
 	}
 
+	bool online = false;
 	for (i = 0; i < argc; i++)
-		if (dev_mounted(argv[i]))
-			goto online;
+		if (dev_mounted(argv[i])) {
+			online = true;
+			break;
+		}
 
-	struct bch_fs *c = bch2_fs_open(argv, argc, open_opts);
-	if (IS_ERR(c)) {
-		fprintf(stderr, "error opening %s: %s\n", argv[0], bch2_err_str(PTR_ERR(c)));
-		exit(EXIT_FAILURE);
-	}
+	if (!online) {
+		struct bch_opts open_opts = bch2_opts_empty();
+		opt_set(open_opts, nostart, true);
 
-	for (i = 0; i < bch2_opts_nr; i++) {
-		u64 v = bch2_opt_get_by_id(&new_opts, i);
+		struct bch_fs *c = bch2_fs_open(argv, argc, open_opts);
+		if (IS_ERR(c)) {
+			fprintf(stderr, "error opening %s: %s\n", argv[0], bch2_err_str(PTR_ERR(c)));
+			exit(EXIT_FAILURE);
+		}
 
-		if (!bch2_opt_defined_by_id(&new_opts, i))
-			continue;
+		mutex_lock(&c->sb_lock);
 
-		ret = bch2_opt_check_may_set(c, i, v);
-		if (ret < 0) {
-			fprintf(stderr, "error setting %s: %i\n",
-				bch2_opt_table[i].attr.name, ret);
-			break;
+		for (i = 0; i < bch2_opts_nr; i++) {
+			const struct bch_option *opt = bch2_opt_table + i;
+
+			u64 v = bch2_opt_get_by_id(&new_opts, i);
+
+			if (!bch2_opt_defined_by_id(&new_opts, i))
+				continue;
+
+			ret = bch2_opt_check_may_set(c, i, v);
+			if (ret < 0) {
+				fprintf(stderr, "error setting %s: %i\n", opt->attr.name, ret);
+				continue;
+			}
+
+			if (!(opt->flags & (OPT_FS|OPT_DEVICE)))
+				fprintf(stderr, "Can't set option %s\n", opt->attr.name);
+
+			if (opt->flags & OPT_FS) {
+				__bch2_opt_set_sb(c->disk_sb.sb, -1, opt, v);
+			}
+
+			if (opt->flags & OPT_DEVICE) {
+				for (unsigned dev = 0; dev < argc; dev++) {
+					int dev_idx = name_to_dev_idx(c, argv[dev]);
+					if (dev_idx < 0) {
+						fprintf(stderr, "Couldn't look up device %s\n", argv[i]);
+						continue;
+					}
+
+					__bch2_opt_set_sb(c->disk_sb.sb, dev_idx, opt, v);
+				}
+			}
 		}
 
-		bch2_opt_set_sb(c, bch2_opt_table + i, v);
-		bch2_opt_set_by_id(&c->opts, i, v);
-	}
+		bch2_write_super(c);
+		mutex_unlock(&c->sb_lock);
 
-	bch2_fs_stop(c);
-	return ret;
-online:
-	{
+		bch2_fs_stop(c);
+		return ret;
+	} else {
 		unsigned dev_idx;
 		struct bchfs_handle fs = bchu_fs_open_by_dev(argv[i], &dev_idx);
 
+		for (i = 0; i < argc; i++) {
+			struct bchfs_handle fs2 = bchu_fs_open_by_dev(argv[i], &dev_idx);
+			if (memcmp(&fs.uuid, &fs2.uuid, sizeof(fs2.uuid)))
+				die("Filesystem mounted, but not all devices are members");
+			bcache_fs_close(fs2);
+		}
+
 		for (i = 0; i < bch2_opts_nr; i++) {
 			if (!new_opt_strs.by_id[i])
 				continue;
 
-			char *path = mprintf("options/%s", bch2_opt_table[i].attr.name);
+			const struct bch_option *opt = bch2_opt_table + i;
+
+			if (!(opt->flags & (OPT_FS|OPT_DEVICE)))
+				fprintf(stderr, "Can't set option %s\n", opt->attr.name);
+
+			if (opt->flags & OPT_FS) {
+				char *path = mprintf("options/%s", opt->attr.name);
+
+				write_file_str(fs.sysfs_fd, path, new_opt_strs.by_id[i]);
+				free(path);
+			}
+
+			if (opt->flags & OPT_DEVICE) {
+				for (unsigned dev = 0; dev < argc; dev++) {
+					struct bchfs_handle fs2 = bchu_fs_open_by_dev(argv[i], &dev_idx);
+					bcache_fs_close(fs2);
+
 
-			write_file_str(fs.sysfs_fd, path, new_opt_strs.by_id[i]);
-			free(path);
+					char *path = mprintf("dev-%u/%s", dev_idx, opt->attr.name);
+					write_file_str(fs.sysfs_fd, path, new_opt_strs.by_id[i]);
+					free(path);
+				}
+			}
 		}
 	}
 	return 0;