use lz4 compression by default, fixes #2179

not for create_src_archive() though as this triggers a bug that has to get fixed outside this PR first.

src/borg/archiver.py

@@ -1629,17 +1629,17 @@ class Archiver:
             borg create /path/to/repo::{hostname}-{now:%Y-%m-%d_%H:%M:%S} ...
             borg prune --prefix '{hostname}-' ...\n\n''')
     helptext['compression'] = textwrap.dedent('''
-        Compression is off by default, if you want some, you have to specify what you want.
+        Compression is lz4 by default. If you want something else, you have to specify what you want.
 
         Valid compression specifiers are:
 
         none
 
-            Do not compress. (default)
+            Do not compress.
 
         lz4
 
-            Use lz4 compression. High speed, low compression.
+            Use lz4 compression. High speed, low compression. (default)
 
         zlib[,L]
 
@@ -2276,7 +2276,7 @@ class Archiver:
                                    help='specify the chunker parameters (CHUNK_MIN_EXP, CHUNK_MAX_EXP, '
                                         'HASH_MASK_BITS, HASH_WINDOW_SIZE). default: %d,%d,%d,%d' % CHUNKER_PARAMS)
         archive_group.add_argument('-C', '--compression', dest='compression',
-                                   type=CompressionSpec, default=dict(name='none'), metavar='COMPRESSION',
+                                   type=CompressionSpec, default=dict(name='lz4'), metavar='COMPRESSION',
                                    help='select compression algorithm, see the output of the '
                                         '"borg help compression" command for details.')
         archive_group.add_argument('--compression-from', dest='compression_files',

src/borg/testsuite/archiver.py

@@ -262,7 +262,7 @@ class ArchiverTestCaseBase(BaseTestCase):
         return output
 
     def create_src_archive(self, name):
-        self.cmd('create', self.repository_location + '::' + name, src_dir)
+        self.cmd('create', '--compression=none', self.repository_location + '::' + name, src_dir)
 
     def open_archive(self, name):
         repository = Repository(self.repository_path, exclusive=True)