diff --git a/strax/corrections.py b/strax/corrections.py
index a6e33b1d2..8c9497fcb 100644
--- a/strax/corrections.py
+++ b/strax/corrections.py
@@ -67,8 +67,10 @@ def read(self, correction):
         del df['_id']
 
         df['time'] = pd.to_datetime(df['time'], utc=True)
-
-        return df.set_index('time')
+        df = df.set_index('time')
+        df = df.sort_index()
+                     
+        return df
 
     def interpolate(self, what, when, how='interpolate', **kwargs):
         """
diff --git a/strax/plugin.py b/strax/plugin.py
index 03eb4c414..84e965e0d 100644
--- a/strax/plugin.py
+++ b/strax/plugin.py
@@ -180,8 +180,18 @@ def __repr__(self):
         return self.__class__.__name__
 
     def dtype_for(self, data_type):
+        """
+        Provide the dtype of one of the provide arguments of the plugin.
+        NB: does not simply provide the dtype of any datatype but must
+        be one of the provide arguments known to the plugin.
+        """
         if self.multi_output:
-            return self.dtype[data_type]
+            if data_type in self.dtype:
+                return self.dtype[data_type]
+            else:
+                raise ValueError(f'dtype_for provides the dtype of one of the '
+                                 f'provide datatypes specified in this plugin '
+                                 f'{data_type} is not provided by this plugin')
         return self.dtype
 
     def can_rechunk(self, data_type):
diff --git a/strax/run_selection.py b/strax/run_selection.py
index ef9ab3f3b..f543e08bc 100644
--- a/strax/run_selection.py
+++ b/strax/run_selection.py
@@ -209,9 +209,13 @@ def select_runs(self, run_mode=None, run_id=None,
     for d in have_available:
         if not d + '_available' in dsets.columns:
             # Get extra availability info from the run db
-            self.runs[d + '_available'] = np.in1d(
-                self.runs.name.values,
-                self.list_available(d))
+            d_available = np.in1d(self.runs.name.values,
+                                  self.list_available(d))
+            # Save both in the context and for this selection using
+            # available = ('data_type',)
+            self.runs[d + '_available'] = d_available
+            dsets[d + '_available'] = d_available
+    for d in have_available:
         dsets = dsets[dsets[d + '_available']]
 
     return dsets
diff --git a/strax/storage/common.py b/strax/storage/common.py
index 867ccfbbe..82ccaddbe 100644
--- a/strax/storage/common.py
+++ b/strax/storage/common.py
@@ -126,6 +126,19 @@ def __init__(self,
         self.readonly = readonly
         self.log = logging.getLogger(self.__class__.__name__)
 
+    def __str__(self):
+        return self.__repr__()
+
+    def __repr__(self):
+        # List the relevant attributes ('path' is actually for the
+        # strax.DataDirectory but it makes more sense to put it here).
+        attributes = ('readonly', 'path', 'exclude', 'take_only')
+        representation = f'{self.__class__.__module__}.{self.__class__.__name__}'
+        for attr in attributes:
+            if hasattr(self, attr) and getattr(self, attr):
+                representation += f', {attr}: {getattr(self, attr)}'
+        return representation
+
     def loader(self, key: DataKey,
                time_range=None,
                allow_incomplete=False,
diff --git a/strax/storage/mongo.py b/strax/storage/mongo.py
index c1c0bda44..5d563c336 100644
--- a/strax/storage/mongo.py
+++ b/strax/storage/mongo.py
@@ -14,6 +14,7 @@
 from strax import StorageFrontend, StorageBackend, Saver
 from datetime import datetime
 from pytz import utc as py_utc
+from warnings import warn
 export, __all__ = strax.exporter()
 
 
@@ -194,6 +195,11 @@ def _save_chunk(self, data, chunk_info, executor=None):
         """see strax.Saver"""
         chunk_i = chunk_info['chunk_i']
 
+        if getattr(data, 'nbytes') > 10_000_000:
+            warn('Inserting documents of size > 10 MB, this is getting '
+                 'close to the 16 MB document size in mongo',
+                 UserWarning)
+
         aggregate_data = []
         # Remove the numpy structures and parse the data. The dtype
         # information is saved with the metadata so don't worry
@@ -207,9 +213,16 @@ def _save_chunk(self, data, chunk_info, executor=None):
         # Get the document to update, if none available start a new one
         # for this chunk
         chunk_id = self.ids_chunk.get(chunk_i, None)
+
+        # We can fail here if the document is too large to be written
+        # out to mongo. One could do a try: except
+        # pymongo.errors.WriteError: pass, but that potentially leads to
+        # abuse of a Mongo instance going unnoticed.
         if chunk_id is not None:
+            # In principle this should not end up here as each chunk
+            # should be it's own document unless you re-chunk
             self.col.update_one({'_id': chunk_id},
-                                {'$addToSet': {f'data': aggregate_data}})
+                                {'$push': {f'data': aggregate_data}})
         else:
             # Start a new document, update it with the proper information
             doc = self.basic_md.copy()
diff --git a/strax/storage/s3.py b/strax/storage/s3.py
index 83f2028d0..3a74ef0fc 100644
--- a/strax/storage/s3.py
+++ b/strax/storage/s3.py
@@ -19,7 +19,7 @@
 import boto3
 from botocore.client import Config
 from botocore.exceptions import ClientError
-
+from warnings import warn
 import strax
 from strax import StorageFrontend
 
@@ -58,6 +58,13 @@ def __init__(self,
 
         super().__init__(*args, **kwargs)
 
+        # S3 storage will be removed in the near future unless one objects in
+        # https://github.com/AxFoundation/strax/issues/307
+        warn('DeprecationWarning S3 storage is not used in strax and will be '
+             'removed in 2021. If there are objections please refer to '
+             'https://github.com/AxFoundation/strax/issues/307',
+             DeprecationWarning)
+
         # Get S3 protocol credentials
         if s3_access_key_id is None:
             if 'S3_ACCESS_KEY_ID' not in os.environ: