diff --git a/zfs_smart_snapshot/main.py b/zfs_smart_snapshot/main.py
index db5c27f..d5ec61b 100644
--- a/zfs_smart_snapshot/main.py
+++ b/zfs_smart_snapshot/main.py
@@ -1,8 +1,12 @@
 from datetime import datetime, timezone
 from dateutil.relativedelta import relativedelta
-from pprint import pprint
 import subprocess
 import sys
+from pprint import pprint
+
+# TODO: Argument parsing
+verbose = True
+dry_run = False
 
 
 def keep_time(now, snapshots, convert, delta, count):
@@ -11,9 +15,10 @@ def keep_time(now, snapshots, convert, delta, count):
         return keep
     start = convert(now) - delta*(count-1)
     for snapshot in snapshots:
-        if snapshot >= start:
+        snapdate = datetime.strptime(snapshot, 'zfs-smart-snap-%Y-%m-%d-%H%M').replace(tzinfo=timezone.utc)
+        if snapdate >= start:
             keep.add(snapshot)
-            start = convert(snapshot) + delta
+            start = convert(snapdate) + delta
         if start > now:
             break
     return keep
@@ -49,7 +54,7 @@ def snapshots_to_keep(now, snapshots, yearly=0, monthly=0, daily=0, hourly=0, fr
     keep.update(keep_day(now, snapshots, daily))
     keep.update(keep_hour(now, snapshots, hourly))
     keep.update(keep_frequent(now, snapshots, frequently))
-    return sorted(list(keep))
+    return keep
 
 
 def parse_int(fields, name, fieldname):
@@ -59,14 +64,13 @@ def parse_int(fields, name, fieldname):
         return int(fields[fieldname])
     except ValueError:
         print(f"Warning: Could not parse value {fields[fieldname]} for fs/zvol {name} prop {fieldname}",
-              output=sys.stderr)
+              file=sys.stderr)
         return -1
 
 
 def zfs_list(fieldnames, args):
     proc = subprocess.run(['/usr/sbin/zfs', 'list', '-H', '-o', ','.join(['name'] + fieldnames)] + args,
                           capture_output=True, check=True, encoding='UTF-8')
-    pprint(proc.args)
     if not fieldnames:
         result = list()
     else:
@@ -96,7 +100,6 @@ def read_snapshots(fs_to_snap):
     result = dict()
     for name in raw_list:
         fs, snap = name.split('@')
-        print(f'{fs}, {snap}')
         if snap.startswith('zfs-smart-snap'):
             result[fs] = result.get(fs, []) + [snap]
     return result
@@ -113,25 +116,53 @@ def find_latest_snapshots(existing_snaps):
 def written_since_last(fs, snap):
     proc = subprocess.run(['/usr/sbin/zfs', 'list', '-Hp', '-o', f'written@{snap}', fs],
                           check=True, capture_output=True, encoding="UTF-8")
-    return int(proc.stdout) > 0
+    res = int(proc.stdout)
+    if verbose and res == 0:
+            print(f"{fs} not written since {snap}, skipping")
+    return res > 0
 
 
 def main():
     now = datetime.now(timezone.utc).replace(second=0, microsecond=0)
+    if verbose:
+        print(f"zfs_smart_snapshot running at {now.strftime('%Y-%m-%d-%H%M')}")
     props = read_snapshot_props()
-    pprint(props)
     fs_to_snap = [k for k, v in props.items() if v['snapshot']]
     if fs_to_snap:
         existing_snaps = read_snapshots(fs_to_snap)
-        pprint(existing_snaps)
         latest_snaps = find_latest_snapshots(existing_snaps)
         fs_to_really_snap = [fs for fs in fs_to_snap if fs not in latest_snaps or
                              written_since_last(fs, latest_snaps[fs])]
         if fs_to_really_snap:
+            pools = {fs.split('/')[0] for fs in fs_to_really_snap}
             snapname = 'zfs-smart-snap-' + now.strftime('%Y-%m-%d-%H%M')
-            subprocess.run(['/usr/sbin/zfs', 'snapshot'] + [f'{fs}@{snapname}' for fs in fs_to_really_snap], check=True)
+            snaps_to_create = [f'{fs}@{snapname}' for fs in fs_to_really_snap]
+            if dry_run or verbose:
+                phrase = "Would" if dry_run else "Will"
+                print(f"{phrase} create snapshots " + ", ".join(snaps_to_create))
+            if not dry_run:
+                for pool in pools:
+                    subprocess.run(['/usr/sbin/zfs', 'snapshot'] + [snap for snap in snaps_to_create if snap.startswith(pool)], check=True)
+            for fs in fs_to_really_snap:
+                existing_snaps[fs] = existing_snaps.get(fs, []) + [snapname]
 
-    # TODO: Cleanup expired snapshots
+        to_delete = []
+        for fs in (fs for fs in fs_to_snap if fs in existing_snaps):
+            to_keep = snapshots_to_keep(now, existing_snaps[fs], props[fs]['yearly'], props[fs]['monthly'], props[fs]['daily'], props[fs]['hourly'], props[fs]['frequently'])
+            # Always keep latest snapshot. If it would be deleted (e.g. due to a incoherent snapshot history configuration) this could confuse the
+            # 'written since last snapshot' logic and cause a cycle of creating/deleteing/creating the snapshot on an idle file system
+            if existing_snaps[fs][-1] not in to_keep:
+                print(f"Warning: Latest snap {fs}@{existing_snaps[fs][-1]} not preserved by retention policy, keeping anyways", file=sys.stderr)
+                to_keep.add(existing_snaps[fs][-1])
+            to_delete += (f'{fs}@{snap}' for snap in set(existing_snaps[fs]).difference(to_keep))
+
+        if not dry_run:
+            if verbose and len(to_delete) > 0:
+                print("Will destroy snapshots " + ", ".join(sorted(to_delete)))
+            for delete_snap in to_delete:
+                subprocess.run(['/usr/sbin/zfs', 'destroy', delete_snap], check=True)
+        elif len(to_delete) > 0:
+            print("Would destroy snapshots " + ", ".join(sorted(to_delete)))
 
 
 if __name__ == "__main__":