diff --git a/compress_logger/compress.py b/compress_logger/compress.py
index 50a35d8..4a880e4 100644
--- a/compress_logger/compress.py
+++ b/compress_logger/compress.py
@@ -26,21 +26,21 @@ def zcat_compress(gzfile, files):
 def zcat_expand(gzfile):
     with gzip.open(gzfile) as f:
         line = f.readline()
-        assert(line.startswith('ZCAT'))
+        assert(line.startswith(b'ZCAT'))
         line = f.readline()
         n = 0
         m = 0
-        while line != '':
-            size, filename = line[:-1].split(' ',1)
+        while line != b'':
+            size, filename = line[:-1].split(b' ',1)
             content = f.read(int(size))
             try:
-                with open(filename) as g:
+                with open(filename, 'rb') as g:
                     c = g.read()
                 if content != c:
                     print('%s does not match' % filename)
                 m += 1
             except IOError:
-                with open(filename, 'w') as g:
+                with open(filename, 'wb') as g:
                     g.write(content)
                 n += 1
             line = f.readline()
@@ -51,7 +51,7 @@ def instdir(instrument=''):
     if instrument != '':
         instrument += '/'
     return '%s/sea/%s' % (os.path.expanduser("~"), instrument)
-        
+
 def compress(logdir, gzdir, variable):
     os.chdir(logdir + variable)
     if not os.path.isdir(gzdir):
@@ -92,7 +92,10 @@ def treat(action, instrument='', years='past', vars=None):
     for year in yrs:
         logdir = logbase + year + '/'
         gzdir = gzbase + year + '/'
-        os.chdir(logdir)
+        if action == COMPRESS:
+            os.chdir(logdir)
+        else:
+            os.chdir(gzdir)
         if not vars:
             varlist = list(glob('*'))
         else:
@@ -105,7 +108,9 @@ def treat(action, instrument='', years='past', vars=None):
                         compress(logdir, gzdir, variable)
                         time.sleep(min(1.0, time.time()-t0)) # be nice
             elif action == EXPAND:
-                os.makedirs(logdir+variable)
+                if variable.endswith('.gz'):
+                    variable = variable[:-3]
+                os.makedirs(logdir+variable, exist_ok=True)
                 print(gzdir, variable, '.gz')
                 if os.path.isfile(gzdir + variable + '.gz'):
                     expand(logdir, gzdir, variable)
diff --git a/compress_logger/lz4.py b/compress_logger/lz4.py
new file mode 100644
index 0000000..71bf363
--- /dev/null
+++ b/compress_logger/lz4.py
@@ -0,0 +1,104 @@
+from glob import glob
+import re
+import os
+import sys
+import shutil
+import time
+
+
+def instdir(instrument=''):
+    if instrument != '':
+        instrument += '/'
+    return '%s/sea/%s' % (os.path.expanduser("~"), instrument)
+
+
+COMPRESS = 1
+EXPAND = 2
+
+
+def treat(instrument, yearlimit):
+    logbase = '%slogger/' % instdir(instrument)
+    os.chdir(logbase)
+    print('chdir', logbase)
+    os.makedirs('trash', exist_ok=True)
+    for ynum in range(2007, 2040):
+        year = str(ynum)
+        cyear = f'{year}.tar.lz4'
+        if year < yearlimit:
+            if os.path.exists(year):
+                if os.path.exists(cyear):
+                    print(cyear, 'exists already')
+                else:
+                    os.system(f'tar cf - {year} | lz4 - {cyear}')
+                    print(cyear, 'created')
+                if os.path.exists(f'trash/{year}'):
+                    shutil.rmtree(f'trash/{year}')
+                os.rename(year, f'trash/{year}')
+            else:
+                print('no', year)
+        else:
+            if os.path.exists(cyear):
+                if os.path.exists(year):
+                    print(year, 'exists already')
+                else:
+                    os.system(f'lz4 -d {cyear} | tar xf -')
+                    print(year, 'created')
+                os.rename(cyear, f'trash/{cyear}')
+
+
+if __name__ == '__main__':
+    action = COMPRESS
+    year = time.strftime("%Y")
+    instruments = []
+    cleanup = True
+    for opt in sys.argv[1:]:
+        if opt == '-x':
+            action = EXPAND
+            cleanup = False
+        elif opt == '-c':
+            cleanup = False
+        else:
+            if opt.startswith('2'):
+                year = opt
+            else:
+                instruments.append(opt)
+    if len(instruments) == 0:
+        instruments = ['']
+    for instrument in instruments:
+        if not os.path.isdir(instdir(instrument)):
+            raise ValueError('%s is not an instrument on this machine' % instrument)
+    removedirs = (
+        'device.force_status_save',
+        'nv.autoflow.*buf',
+        'nv.autoflow.*min',
+        'nv.autoflow.*max',
+        'table.val_*',
+        '*.*.stddev',
+        'device.ccu4version',
+        'cc.f',
+        'cc.nfb',
+        'cc.hfb',
+        'graph_*',
+    )
+    print("instruments: %s" % ", ".join(instruments))
+    print("compress years before %s" % year)
+    for instrument in instruments:
+        print('instrument:', instdir(instrument))
+        if cleanup:
+            for pat in removedirs:
+                print('remove', pat)
+                gap = 0
+                t0 = time.time()
+                t1 = t0
+                for dir in glob(instdir(instrument)+'logger/*/'+pat):
+                    shutil.rmtree(dir)
+                    now = time.time()
+                    if now > t0 + 5:
+                        if gap > 0:
+                            print("+%d" % gap)
+                        print(dir)
+                    else:
+                        gap += 1
+                    time.sleep(min(1.0, now - t1)) # be nice
+                    t1 = now
+        treat(instrument, year)