diff --git a/tests/test_btree.toml b/tests/test_btree.toml
index 79e72b6d..10cc9a20 100644
--- a/tests/test_btree.toml
+++ b/tests/test_btree.toml
@@ -415,7 +415,7 @@ code = '''
 
 [cases.test_btree_push_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 in = 'lfs.c'
 code = '''
     lfs_t lfs;
@@ -576,7 +576,7 @@ code = '''
 [cases.test_btree_push_sparse_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.W = 5
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 in = 'lfs.c'
 code = '''
     lfs_t lfs;
@@ -971,7 +971,7 @@ code = '''
 [cases.test_btree_update_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.SAMPLES = 10
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 in = 'lfs.c'
 code = '''
     lfs_t lfs;
@@ -1163,7 +1163,7 @@ code = '''
 [cases.test_btree_update_sparse_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.W = 5
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 in = 'lfs.c'
 code = '''
     lfs_t lfs;
@@ -1813,7 +1813,7 @@ code = '''
 [cases.test_btree_pop_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.REMAINING = [64, 2, 1, 0]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 if = 'N > REMAINING'
 in = 'lfs.c'
 code = '''
@@ -2040,7 +2040,7 @@ code = '''
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.W = 5
 defines.REMAINING = [64, 2, 1, 0]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 if = 'N > REMAINING'
 in = 'lfs.c'
 code = '''
@@ -2270,7 +2270,7 @@ code = '''
 
 [cases.test_btree_split_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 in = 'lfs.c'
 code = '''
     lfs_t lfs;
@@ -2430,7 +2430,7 @@ code = '''
 [cases.test_btree_split_sparse_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.W = 5
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 in = 'lfs.c'
 code = '''
     lfs_t lfs;
@@ -3593,7 +3593,7 @@ code = '''
 
 [cases.test_btree_find_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 in = 'lfs.c'
 code = '''
     lfs_t lfs;
@@ -3792,7 +3792,7 @@ code = '''
 [cases.test_btree_find_sparse_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.W = 5
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 in = 'lfs.c'
 code = '''
     lfs_t lfs;
@@ -4481,7 +4481,7 @@ code = '''
 
 [cases.test_btree_traversal_fuzz]
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 in = 'lfs.c'
 code = '''
     lfs_t lfs;
diff --git a/tests/test_dirs.toml b/tests/test_dirs.toml
index cf88ec82..8a8d4e1a 100644
--- a/tests/test_dirs.toml
+++ b/tests/test_dirs.toml
@@ -742,7 +742,7 @@ code = '''
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.REMOUNT = [false, true]
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 32'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
@@ -825,7 +825,7 @@ code = '''
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.REMOUNT = [false, true]
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 32'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
@@ -1280,9 +1280,9 @@ code = '''
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.PARENT = [false, true]
 defines.REMOUNT = [false, true]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 64'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
@@ -3283,7 +3283,7 @@ defines.REMOUNT = [false, true]
 if = [
     'N > REMAINING',
     # limit powerloss testing due to time
-    '!TEST_PLS || N <= 32',
+    '!TEST_PLS || N <= 16',
 ]
 reentrant = true
 code = '''
@@ -3406,7 +3406,7 @@ defines.REMOUNT = [false, true]
 if = [
     'N > REMAINING',
     # limit powerloss testing due to time
-    '!TEST_PLS || N <= 32',
+    '!TEST_PLS || N <= 16',
 ]
 reentrant = true
 code = '''
@@ -4203,9 +4203,9 @@ code = '''
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.PARENT = [false, true]
 defines.REMOUNT = [false, true]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 64'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
@@ -5735,7 +5735,7 @@ defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.BEFORE = [false, true]
 defines.REMOUNT = [false, true]
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 32'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
@@ -5858,7 +5858,7 @@ defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.BEFORE = [false, true]
 defines.REMOUNT = [false, true]
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 32'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
@@ -6671,9 +6671,9 @@ code = '''
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.PARENT = [false, true]
 defines.REMOUNT = [false, true]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 64'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
@@ -6816,9 +6816,9 @@ code = '''
 defines.N = [1, 2, 4, 8, 16, 32, 64, 128, 256, 512]
 defines.PARENT = [false, true]
 defines.REMOUNT = [false, true]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 64'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
diff --git a/tests/test_dread.toml b/tests/test_dread.toml
index 7eba40ed..d47314bb 100644
--- a/tests/test_dread.toml
+++ b/tests/test_dread.toml
@@ -1496,7 +1496,7 @@ defines.PARENT = [false, true]
 # SEEK=2 => rewind then seek
 defines.SEEK = [0, 1, 2]
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 32'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
@@ -1631,7 +1631,7 @@ defines.PARENT = [0, 1, 2]
 # SEEK=2 => rewind then seek
 defines.SEEK = [0, 1, 2]
 # limit powerloss testing due to time
-if = '!TEST_PLS || N <= 32'
+if = '!TEST_PLS || N <= 16'
 reentrant = true
 code = '''
     // format once per test
diff --git a/tests/test_files.toml b/tests/test_files.toml
index 8593d979..a78bee9c 100644
--- a/tests/test_files.toml
+++ b/tests/test_files.toml
@@ -772,7 +772,7 @@ defines.SIZE = [
     '4*BLOCK_SIZE',
 ]
 defines.REMOUNT = [false, true]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 if = '(SIZE*N)/BLOCK_SIZE <= 32'
 code = '''
     lfs_t lfs;
@@ -1122,7 +1122,7 @@ defines.SIZE = [
     '4*BLOCK_SIZE',
 ]
 defines.REMOUNT = [false, true]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 if = '(SIZE*N)/BLOCK_SIZE <= 32'
 code = '''
     lfs_t lfs;
@@ -2058,7 +2058,7 @@ defines.SIZE = [
     '4*BLOCK_SIZE',
 ]
 defines.REMOUNT = [false, true]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 if = '(SIZE*N)/BLOCK_SIZE <= 32'
 code = '''
     lfs_t lfs;
@@ -2252,7 +2252,7 @@ defines.SIZE = [
     '4*BLOCK_SIZE',
 ]
 defines.REMOUNT = [false, true]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 if = '(SIZE*N)/BLOCK_SIZE <= 32'
 code = '''
     lfs_t lfs;
diff --git a/tests/test_fsync.toml b/tests/test_fsync.toml
index 5a3668e6..83fcad29 100644
--- a/tests/test_fsync.toml
+++ b/tests/test_fsync.toml
@@ -534,7 +534,7 @@ code = '''
 
 [cases.test_fsync_rrrr_fuzz]
 defines.R = 4
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 20
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -687,7 +687,7 @@ defines.SYNC = [0, 1, 2]
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 20
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -873,7 +873,7 @@ defines.SYNC = [0, 1, 2]
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 20
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -1066,7 +1066,7 @@ defines.SYNC = [0, 1, 2]
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 20
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -1279,7 +1279,7 @@ defines.SYNC = [0, 1, 2]
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 20
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -1391,7 +1391,7 @@ defines.SYNC = [0, 1, 2]
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 40
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -1525,7 +1525,7 @@ defines.SYNC = [0, 1, 2]
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 40
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -2426,7 +2426,7 @@ defines.SYNC = [0, 1, 2]
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 20
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -2619,7 +2619,7 @@ defines.SYNC = [0, 1, 2]
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 20
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -2827,7 +2827,7 @@ defines.SYNC = [0, 1, 2]
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 20
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -2944,7 +2944,7 @@ defines.RW = 4
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 40
 defines.SIZE = [
     'CACHE_SIZE/2',
@@ -3093,7 +3093,7 @@ defines.RW = 4
 # FLUSH=1 => flush via lfsr_file_flush
 # FLUSH=2 => flush via LFS_O_FLUSH
 defines.FLUSH = [0, 1, 2]
-defines.SEED = 'range(10)'
+defines.SEED = 'range(20)'
 defines.N = 40
 defines.SIZE = [
     'CACHE_SIZE/2',
diff --git a/tests/test_fwrite.toml b/tests/test_fwrite.toml
index 3fcf06d0..bb26d1e6 100644
--- a/tests/test_fwrite.toml
+++ b/tests/test_fwrite.toml
@@ -29,8 +29,8 @@ defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -135,8 +135,8 @@ defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -313,8 +313,8 @@ defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -495,7 +495,7 @@ defines.TO = [
 defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
-    # these just save testing time
+    # this just saves testing time
     'FROM / FRAGMENT_SIZE <= 4096',
     'TO / FRAGMENT_SIZE <= 4096',
 ]
@@ -617,7 +617,7 @@ defines.TO = [
 defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
-    # these just save testing time
+    # this just saves testing time
     'FROM / FRAGMENT_SIZE <= 4096',
     'AND / FRAGMENT_SIZE <= 4096',
     'TO / FRAGMENT_SIZE <= 4096',
@@ -749,7 +749,7 @@ defines.TO = [
 defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
-    # these just save testing time
+    # this just saves testing time
     'FROM / FRAGMENT_SIZE <= 4096',
     'TO / FRAGMENT_SIZE <= 4096',
 ]
@@ -875,7 +875,7 @@ defines.TO = [
 defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
-    # these just save testing time
+    # this just saves testing time
     'FROM / FRAGMENT_SIZE <= 4096',
     'AND / FRAGMENT_SIZE <= 4096',
     'TO / FRAGMENT_SIZE <= 4096',
@@ -1011,8 +1011,10 @@ defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
+    # writing backwards is expected to be a bit slow
+    'SIZE <= 4*1024*CHUNK',
 ]
 code = '''
     lfs_t lfs;
@@ -1147,8 +1149,8 @@ defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -1334,8 +1336,8 @@ defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -1520,8 +1522,8 @@ defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -1661,8 +1663,8 @@ defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -1804,8 +1806,8 @@ defines.SIZE = [
 defines.CHUNK = [32, 8]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -1887,8 +1889,8 @@ defines.INIT = [0, 1, 2]
 defines.SYNC = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -2027,8 +2029,8 @@ defines.INIT = [0, 1, 2]
 defines.SYNC = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -2186,8 +2188,8 @@ defines.SIZE = [
 defines.INIT = [0, 1, 2]
 defines.MODE = ['LFS_O_RDONLY', 'LFS_O_WRONLY', 'LFS_O_RDWR']
 if = [
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;
@@ -2291,8 +2293,8 @@ defines.SYNC = [false, true]
 defines.REMOUNT = [false, true]
 if = [
     'CHUNK <= SIZE',
-    # this just save testing time
-    'SIZE / FRAGMENT_SIZE <= 4096',
+    # this just saves testing time
+    'SIZE <= 4*1024*FRAGMENT_SIZE',
 ]
 code = '''
     lfs_t lfs;