diff --git a/Kconfig b/Kconfig
index df3719a4..62381dda 100644
--- a/Kconfig
+++ b/Kconfig
@@ -99,6 +99,25 @@ config MARS_MIN_SPACE
 	---help---
 	Normally ON. Switch off only for EXPERIMENTS!
 
+config MARS_MIN_SPACE_BASE
+	int "free space in /mars/ (hard limit in gigabytes)"
+	depends on MARS && MARS_MIN_SPACE
+	default 8
+	---help---
+	when this limit is exceeded, all write requests to /mars/
+	will stop. This affects not only write IO to /dev/mars/*,
+	but also logfile transfers etc.
+	In order to retain full operations, you _need_ to implement
+	your own monitoring which _must_ warn you long before this
+	hard limit catches you.
+
+config MARS_MIN_SPACE_PERCENT
+	int "free space in /mars/ (hard limit in percent)"
+	depends on MARS && MARS_MIN_SPACE
+	default 0
+	---help---
+	this limit is in addition to CONFIG_MARS_MIN_SPACE_BASE.
+
 config MARS_PREFER_SIO
 	bool "prefer sio bricks instead of aio"
 	depends on MARS
diff --git a/sy_old/mars_light.c b/sy_old/mars_light.c
index ce049d41..14e4f3f6 100644
--- a/sy_old/mars_light.c
+++ b/sy_old/mars_light.c
@@ -119,11 +119,10 @@ struct light_class {
 //#define COPY_APPEND_MODE 1 // FIXME: does not work yet
 #define COPY_PRIO MARS_PRIO_LOW
 
-#define MIN_SPACE (1024 * 1024 * 8) // 8 GB
 #ifdef CONFIG_MARS_MIN_SPACE
-#define EXHAUSTED(x) ((x) <= MIN_SPACE)
+#define EXHAUSTED(x,max) ((x) <= ((max) / 100 * CONFIG_MARS_MIN_SPACE_PERCENT + CONFIG_MARS_MIN_SPACE_BASE * 1024 * 1024))
 #else
-#define EXHAUSTED(x) (false)
+#define EXHAUSTED(x,max) (false)
 #endif
 
 static
@@ -498,6 +497,7 @@ struct mars_rotate {
 	struct mars_dent *prev_log;
 	struct mars_dent *next_log;
 	struct if_brick *if_brick;
+	loff_t total_space;
 	loff_t remaining_space;
 	loff_t copy_end_pos;
 	loff_t start_pos;
@@ -1597,7 +1597,7 @@ int make_log_init(void *buf, struct mars_dent *dent)
 	rot->max_sequence = 0;
 	rot->has_error = false;
 
-	rot->remaining_space = mars_remaining_space(parent_path);
+	mars_remaining_space(parent_path, &rot->total_space, &rot->remaining_space);
 
 	/* Fetch the replay status symlink.
 	 * It must exist, and its value will control everything.
@@ -3428,8 +3428,8 @@ static int light_thread(void *data)
 		_global.global_power.button = !kthread_should_stop();
 		_make_alivelink("alive", _global.global_power.button);
 
-		_global.remaining_space = mars_remaining_space("/mars");
-		exhausted = EXHAUSTED(_global.remaining_space);
+		mars_remaining_space("/mars", &_global.total_space, &_global.remaining_space);
+		exhausted = EXHAUSTED(_global.remaining_space, _global.total_space);
 		_global.exhausted = exhausted;
 		_make_alivelink("exhausted", exhausted);
 		if (exhausted)
diff --git a/sy_old/strategy.h b/sy_old/strategy.h
index 0b38385d..ca9ffcc2 100644
--- a/sy_old/strategy.h
+++ b/sy_old/strategy.h
@@ -53,6 +53,7 @@ struct mars_global {
 	struct list_head brick_anchor;
 	struct list_head server_anchor;
 	wait_queue_head_t main_event;
+	loff_t total_space;
 	loff_t remaining_space;
 	int global_version;
 	volatile bool main_trigger;
@@ -121,7 +122,7 @@ extern int mars_symlink(const char *oldpath, const char *newpath, const struct t
 extern int mars_rename(const char *oldpath, const char *newpath);
 extern int mars_chmod(const char *path, mode_t mode);
 extern int mars_lchown(const char *path, uid_t uid);
-extern loff_t mars_remaining_space(const char *fspath);
+extern void mars_remaining_space(const char *fspath, loff_t *total, loff_t *remaining);
 
 /////////////////////////////////////////////////////////////////////////
 
diff --git a/sy_old/sy_generic.c b/sy_old/sy_generic.c
index 7d2745a8..c7879c60 100644
--- a/sy_old/sy_generic.c
+++ b/sy_old/sy_generic.c
@@ -186,11 +186,31 @@ int mars_lchown(const char *path, uid_t uid)
 }
 EXPORT_SYMBOL_GPL(mars_lchown);
 
-loff_t mars_remaining_space(const char *fspath)
+loff_t _compute_space(struct kstatfs *kstatfs, loff_t raw_val)
+{
+	int fsize = kstatfs->f_frsize;
+	if (fsize <= 0)
+		fsize = kstatfs->f_bsize;
+
+	MARS_INF("fsize = %d raw_val = %lld\n", fsize, raw_val);
+	// illegal values? cannot do anything....
+	if (fsize <= 0)
+		return 0;
+
+	// prevent intermediate integer overflows
+	if (fsize <= 1024)
+		return raw_val / (1024 / fsize);
+
+	return raw_val * (fsize / 1024);
+}
+
+void mars_remaining_space(const char *fspath, loff_t *total, loff_t *remaining)
 {
 	struct path path = {};
 	struct kstatfs kstatfs = {};
-	loff_t res;
+	int res;
+
+	*total = *remaining = 0;
 
 	res = user_path_at(AT_FDCWD, fspath, 0, &path);
 	if (unlikely(res < 0)) {
@@ -208,16 +228,12 @@ loff_t mars_remaining_space(const char *fspath)
 		goto done;
 	}
 
-	/* It seems that most filesystems use KB rather
-	 * than blocks as base unit.
-	 */
-	//res = (loff_t)kstatfs.f_bavail;
-	res = (loff_t)kstatfs.f_bfree;
+	*total = _compute_space(&kstatfs, kstatfs.f_blocks);
+	*remaining = _compute_space(&kstatfs, kstatfs.f_bfree);
 	
 done:
 	path_put(&path);
-err:
-	return res;
+err: ;
 }
 EXPORT_SYMBOL_GPL(mars_remaining_space);