diff --git a/darc/repository.py b/darc/repository.py
new file mode 100644
index 000000000..e38995e0c
--- /dev/null
+++ b/darc/repository.py
@@ -0,0 +1,503 @@
+from configparser import RawConfigParser
+from binascii import hexlify, unhexlify
+import fcntl
+import os
+import re
+import shutil
+import struct
+import tempfile
+import unittest
+from zlib import crc32
+
+from .hashindex import NSIndex
+from .helpers import IntegrityError, read_msgpack, write_msgpack
+from .lrucache import LRUCache
+
+MAX_OBJECT_SIZE = 20 * 1024 * 1024
+
+TAG_PUT = 0
+TAG_DELETE = 1
+TAG_COMMIT = 2
+
+
+class Repository(object):
+    """Filesystem based transactional key value store
+
+    On disk layout:
+    dir/README
+    dir/config
+    dir/data/<X / SEGMENTS_PER_DIR>/<X>
+    dir/index.X
+    dir/hints.X
+    """
+    DEFAULT_MAX_SEGMENT_SIZE = 5 * 1024 * 1024
+    DEFAULT_SEGMENTS_PER_DIR = 10000
+
+    class DoesNotExist(KeyError):
+        """Requested key does not exist"""
+
+    class AlreadyExists(KeyError):
+        """Requested key does not exist"""
+
+    def __init__(self, path, create=False):
+        self.io = None
+        if create:
+            self.create(path)
+        self.open(path)
+
+    def create(self, path):
+        """Create a new empty repository at `path`
+        """
+        if os.path.exists(path) and (not os.path.isdir(path) or os.listdir(path)):
+            raise self.AlreadyExists(path)
+        if not os.path.exists(path):
+            os.mkdir(path)
+        with open(os.path.join(path, 'README'), 'w') as fd:
+            fd.write('This is a DARC repository\n')
+        os.mkdir(os.path.join(path, 'data'))
+        config = RawConfigParser()
+        config.add_section('repository')
+        config.set('repository', 'version', '1')
+        config.set('repository', 'segments_per_dir', self.DEFAULT_SEGMENTS_PER_DIR)
+        config.set('repository', 'max_segment_size', self.DEFAULT_MAX_SEGMENT_SIZE)
+        config.set('repository', 'id', hexlify(os.urandom(32)).decode('ascii'))
+        with open(os.path.join(path, 'config'), 'w') as fd:
+            config.write(fd)
+
+    def open(self, path):
+        self.head = None
+        self.path = path
+        if not os.path.isdir(path):
+            raise self.DoesNotExist(path)
+        self.lock_fd = open(os.path.join(path, 'README'), 'r+')
+        fcntl.flock(self.lock_fd, fcntl.LOCK_EX)
+        self.config = RawConfigParser()
+        self.config.read(os.path.join(self.path, 'config'))
+        if self.config.getint('repository', 'version') != 1:
+            raise Exception('%s Does not look like a darc repository')
+        self.max_segment_size = self.config.getint('repository', 'max_segment_size')
+        self.segments_per_dir = self.config.getint('repository', 'segments_per_dir')
+        self.id = unhexlify(self.config.get('repository', 'id').strip().encode('ascii'))  # .encode needed for Python 3.[0-2]
+        self.rollback()
+
+    def close(self):
+        self.rollback()
+        self.lock_fd.close()
+
+    def commit(self, rollback=True):
+        """Commit transaction
+        """
+        self.io.write_commit()
+        self.compact_segments()
+        self.write_index()
+        self.rollback()
+
+    def _available_indices(self, reverse=False):
+        names = [int(name[6:]) for name in os.listdir(self.path) if re.match('index\.\d+', name)]
+        names.sort(reverse=reverse)
+        return names
+
+    def open_index(self, head, read_only=False):
+        if head is None:
+            self.index = NSIndex.create(os.path.join(self.path, 'index.tmp').encode('utf-8'))
+            self.segments = {}
+            self.compact = set()
+        else:
+            if read_only:
+                self.index = NSIndex((os.path.join(self.path, 'index.%d') % head).encode('utf-8'))
+            else:
+                shutil.copy(os.path.join(self.path, 'index.%d' % head),
+                            os.path.join(self.path, 'index.tmp'))
+                self.index = NSIndex(os.path.join(self.path, 'index.tmp').encode('utf-8'))
+            hints = read_msgpack(os.path.join(self.path, 'hints.%d' % head))
+            if hints[b'version'] != 1:
+                raise ValueError('Unknown hints file version: %d' % hints['version'])
+            self.segments = hints[b'segments']
+            self.compact = set(hints[b'compact'])
+
+    def write_index(self):
+        hints = {b'version': 1,
+                 b'segments': self.segments,
+                 b'compact': list(self.compact)}
+        write_msgpack(os.path.join(self.path, 'hints.%d' % self.io.head), hints)
+        self.index.flush()
+        os.rename(os.path.join(self.path, 'index.tmp'),
+                  os.path.join(self.path, 'index.%d' % self.io.head))
+        # Remove old indices
+        current = '.%d' % self.io.head
+        for name in os.listdir(self.path):
+            if not name.startswith('index.') and not name.startswith('hints.'):
+                continue
+            if name.endswith(current):
+                continue
+            os.unlink(os.path.join(self.path, name))
+
+    def compact_segments(self):
+        """Compact sparse segments by copying data into new segments
+        """
+        if not self.compact:
+            return
+
+        def lookup(tag, key):
+            return tag == TAG_PUT and self.index.get(key, (-1, -1))[0] == segment
+        segments = self.segments
+        for segment in sorted(self.compact):
+            if segments[segment] > 0:
+                for tag, key, data in self.io.iter_objects(segment, lookup, include_data=True):
+                    new_segment, offset = self.io.write_put(key, data)
+                    self.index[key] = new_segment, offset
+                    segments.setdefault(new_segment, 0)
+                    segments[new_segment] += 1
+                    segments[segment] -= 1
+                assert segments[segment] == 0
+        self.io.write_commit()
+        for segment in self.compact:
+            assert self.segments.pop(segment) == 0
+            self.io.delete_segment(segment)
+        self.compact = set()
+
+    def recover(self, path):
+        """Recover missing index by replaying logs"""
+        start = None
+        available = self._available_indices()
+        if available:
+            start = available[-1]
+        self.open_index(start)
+        for segment, filename in self.io._segment_names():
+            if start is not None and segment <= start:
+                continue
+            self.segments[segment] = 0
+            for tag, key, offset in self.io.iter_objects(segment):
+                if tag == TAG_PUT:
+                    try:
+                        s, _ = self.index[key]
+                        self.compact.add(s)
+                        self.segments[s] -= 1
+                    except KeyError:
+                        pass
+                    self.index[key] = segment, offset
+                    self.segments[segment] += 1
+                elif tag == TAG_DELETE:
+                    try:
+                        s, _ = self.index.pop(key)
+                        self.segments[s] -= 1
+                        self.compact.add(s)
+                        self.compact.add(segment)
+                    except KeyError:
+                        pass
+            if self.segments[segment] == 0:
+                self.compact.add(segment)
+        if self.io.head is not None:
+            self.write_index()
+
+    def rollback(self):
+        """
+        """
+        self._active_txn = False
+        if self.io:
+            self.io.close()
+        self.io = LoggedIO(self.path, self.max_segment_size, self.segments_per_dir)
+        if self.io.head is not None and not os.path.exists(os.path.join(self.path, 'index.%d' % self.io.head)):
+            self.recover(self.path)
+        self.open_index(self.io.head, read_only=True)
+
+    def _len(self):
+        return len(self.index)
+
+    def get(self, id):
+        try:
+            segment, offset = self.index[id]
+            return self.io.read(segment, offset, id)
+        except KeyError:
+            raise self.DoesNotExist
+
+    def get_many(self, ids, peek=None):
+        for id in ids:
+            yield self.get(id)
+
+    def put(self, id, data, wait=True):
+        if not self._active_txn:
+            self._active_txn = True
+            self.open_index(self.io.head)
+        try:
+            segment, _ = self.index[id]
+            self.segments[segment] -= 1
+            self.compact.add(segment)
+            segment = self.io.write_delete(id)
+            self.segments.setdefault(segment, 0)
+            self.compact.add(segment)
+        except KeyError:
+            pass
+        segment, offset = self.io.write_put(id, data)
+        self.segments.setdefault(segment, 0)
+        self.segments[segment] += 1
+        self.index[id] = segment, offset
+
+    def delete(self, id, wait=True):
+        if not self._active_txn:
+            self._active_txn = True
+            self.open_index(self.io.head)
+        try:
+            segment, offset = self.index.pop(id)
+            self.segments[segment] -= 1
+            self.compact.add(segment)
+            segment = self.io.write_delete(id)
+            self.compact.add(segment)
+            self.segments.setdefault(segment, 0)
+        except KeyError:
+            raise self.DoesNotExist
+
+    def add_callback(self, cb, data):
+        cb(None, None, data)
+
+
+class LoggedIO(object):
+
+    header_fmt = struct.Struct('<IIB')
+    assert header_fmt.size == 9
+    put_header_fmt = struct.Struct('<IIB32s')
+    assert put_header_fmt.size == 41
+    header_no_crc_fmt = struct.Struct('<IB')
+    assert header_no_crc_fmt.size == 5
+    crc_fmt = struct.Struct('<I')
+    assert crc_fmt.size == 4
+
+    _commit = header_no_crc_fmt.pack(9, TAG_COMMIT)
+    COMMIT = crc_fmt.pack(crc32(_commit)) + _commit
+
+    def __init__(self, path, limit, segments_per_dir, capacity=100):
+        self.path = path
+        self.fds = LRUCache(capacity)
+        self.segment = None
+        self.limit = limit
+        self.segments_per_dir = segments_per_dir
+        self.offset = 0
+        self._write_fd = None
+        self.head = None
+        self.cleanup()
+
+    def close(self):
+        for segment in list(self.fds.keys()):
+            self.fds.pop(segment).close()
+        self.close_segment()
+        self.fds = None  # Just to make sure we're disabled
+
+    def _segment_names(self, reverse=False):
+        for dirpath, dirs, filenames in os.walk(os.path.join(self.path, 'data')):
+            dirs.sort(key=int, reverse=reverse)
+            filenames.sort(key=int, reverse=reverse)
+            for filename in filenames:
+                yield int(filename), os.path.join(dirpath, filename)
+
+    def cleanup(self):
+        """Delete segment files left by aborted transactions
+        """
+        self.head = None
+        self.segment = 0
+        for segment, filename in self._segment_names(reverse=True):
+            if self.is_complete_segment(filename):
+                self.head = segment
+                self.segment = self.head + 1
+                return
+            else:
+                os.unlink(filename)
+
+    def is_complete_segment(self, filename):
+        with open(filename, 'rb') as fd:
+            fd.seek(-self.header_fmt.size, 2)
+            return fd.read(self.header_fmt.size) == self.COMMIT
+
+    def segment_filename(self, segment):
+        return os.path.join(self.path, 'data', str(segment // self.segments_per_dir), str(segment))
+
+    def get_write_fd(self, no_new=False):
+        if not no_new and self.offset and self.offset > self.limit:
+            self.close_segment()
+        if not self._write_fd:
+            if self.segment % self.segments_per_dir == 0:
+                dirname = os.path.join(self.path, 'data', str(self.segment // self.segments_per_dir))
+                if not os.path.exists(dirname):
+                    os.mkdir(dirname)
+            self._write_fd = open(self.segment_filename(self.segment), 'ab')
+            self._write_fd.write(b'DSEGMENT')
+            self.offset = 8
+        return self._write_fd
+
+    def get_fd(self, segment):
+        try:
+            return self.fds[segment]
+        except KeyError:
+            fd = open(self.segment_filename(segment), 'rb')
+            self.fds[segment] = fd
+            return fd
+
+    def delete_segment(self, segment):
+        try:
+            os.unlink(self.segment_filename(segment))
+        except OSError:
+            pass
+
+    def iter_objects(self, segment, lookup=None, include_data=False):
+        fd = self.get_fd(segment)
+        fd.seek(0)
+        if fd.read(8) != b'DSEGMENT':
+            raise IntegrityError('Invalid segment header')
+        offset = 8
+        header = fd.read(self.header_fmt.size)
+        while header:
+            crc, size, tag = self.header_fmt.unpack(header)
+            if size > MAX_OBJECT_SIZE:
+                raise IntegrityError('Invalid segment object size')
+            rest = fd.read(size - self.header_fmt.size)
+            if crc32(rest, crc32(memoryview(header)[4:])) & 0xffffffff != crc:
+                raise IntegrityError('Segment checksum mismatch')
+            if tag not in (TAG_PUT, TAG_DELETE, TAG_COMMIT):
+                raise IntegrityError('Invalid segment entry header')
+            key = None
+            if tag in (TAG_PUT, TAG_DELETE):
+                key = rest[:32]
+            if not lookup or lookup(tag, key):
+                if include_data:
+                    yield tag, key, rest[32:]
+                else:
+                    yield tag, key, offset
+            offset += size
+            header = fd.read(self.header_fmt.size)
+
+    def read(self, segment, offset, id):
+        if segment == self.segment:
+            self._write_fd.flush()
+        fd = self.get_fd(segment)
+        fd.seek(offset)
+        header = fd.read(self.put_header_fmt.size)
+        crc, size, tag, key = self.put_header_fmt.unpack(header)
+        if size > MAX_OBJECT_SIZE:
+            raise IntegrityError('Invalid segment object size')
+        data = fd.read(size - self.put_header_fmt.size)
+        if crc32(data, crc32(memoryview(header)[4:])) & 0xffffffff != crc:
+            raise IntegrityError('Segment checksum mismatch')
+        if tag != TAG_PUT or id != key:
+            raise IntegrityError('Invalid segment entry header')
+        return data
+
+    def write_put(self, id, data):
+        size = len(data) + self.put_header_fmt.size
+        fd = self.get_write_fd()
+        offset = self.offset
+        header = self.header_no_crc_fmt.pack(size, TAG_PUT)
+        crc = self.crc_fmt.pack(crc32(data, crc32(id, crc32(header))) & 0xffffffff)
+        fd.write(b''.join((crc, header, id, data)))
+        self.offset += size
+        return self.segment, offset
+
+    def write_delete(self, id):
+        fd = self.get_write_fd()
+        header = self.header_no_crc_fmt.pack(self.put_header_fmt.size, TAG_DELETE)
+        crc = self.crc_fmt.pack(crc32(id, crc32(header)) & 0xffffffff)
+        fd.write(b''.join((crc, header, id)))
+        self.offset += self.put_header_fmt.size
+        return self.segment
+
+    def write_commit(self):
+        fd = self.get_write_fd(no_new=True)
+        header = self.header_no_crc_fmt.pack(self.header_fmt.size, TAG_COMMIT)
+        crc = self.crc_fmt.pack(crc32(header) & 0xffffffff)
+        fd.write(b''.join((crc, header)))
+        self.head = self.segment
+        self.close_segment()
+
+    def close_segment(self):
+        if self._write_fd:
+            self.segment += 1
+            self.offset = 0
+            os.fsync(self._write_fd)
+            self._write_fd.close()
+            self._write_fd = None
+
+
+class RepositoryTestCase(unittest.TestCase):
+
+    def open(self, create=False):
+        return Repository(os.path.join(self.tmppath, 'repository'), create=create)
+
+    def setUp(self):
+        self.tmppath = tempfile.mkdtemp()
+        self.repository = self.open(create=True)
+
+    def tearDown(self):
+        self.repository.close()
+        shutil.rmtree(self.tmppath)
+
+    def test1(self):
+        for x in range(100):
+            self.repository.put(('%-32d' % x).encode('ascii'), b'SOMEDATA')
+        key50 = ('%-32d' % 50).encode('ascii')
+        self.assertEqual(self.repository.get(key50), b'SOMEDATA')
+        self.repository.delete(key50)
+        self.assertRaises(Repository.DoesNotExist, lambda: self.repository.get(key50))
+        self.repository.commit()
+        self.repository.close()
+        repository2 = self.open()
+        self.assertRaises(Repository.DoesNotExist, lambda: repository2.get(key50))
+        for x in range(100):
+            if x == 50:
+                continue
+            self.assertEqual(repository2.get(('%-32d' % x).encode('ascii')), b'SOMEDATA')
+        repository2.close()
+
+    def test2(self):
+        """Test multiple sequential transactions
+        """
+        self.repository.put(b'00000000000000000000000000000000', b'foo')
+        self.repository.put(b'00000000000000000000000000000001', b'foo')
+        self.repository.commit()
+        self.repository.delete(b'00000000000000000000000000000000')
+        self.repository.put(b'00000000000000000000000000000001', b'bar')
+        self.repository.commit()
+        self.assertEqual(self.repository.get(b'00000000000000000000000000000001'), b'bar')
+
+    def test_consistency(self):
+        """Test cache consistency
+        """
+        self.repository.put(b'00000000000000000000000000000000', b'foo')
+        self.assertEqual(self.repository.get(b'00000000000000000000000000000000'), b'foo')
+        self.repository.put(b'00000000000000000000000000000000', b'foo2')
+        self.assertEqual(self.repository.get(b'00000000000000000000000000000000'), b'foo2')
+        self.repository.put(b'00000000000000000000000000000000', b'bar')
+        self.assertEqual(self.repository.get(b'00000000000000000000000000000000'), b'bar')
+        self.repository.delete(b'00000000000000000000000000000000')
+        self.assertRaises(Repository.DoesNotExist, lambda: self.repository.get(b'00000000000000000000000000000000'))
+
+    def test_consistency2(self):
+        """Test cache consistency2
+        """
+        self.repository.put(b'00000000000000000000000000000000', b'foo')
+        self.assertEqual(self.repository.get(b'00000000000000000000000000000000'), b'foo')
+        self.repository.commit()
+        self.repository.put(b'00000000000000000000000000000000', b'foo2')
+        self.assertEqual(self.repository.get(b'00000000000000000000000000000000'), b'foo2')
+        self.repository.rollback()
+        self.assertEqual(self.repository.get(b'00000000000000000000000000000000'), b'foo')
+
+    def test_single_kind_transactions(self):
+        # put
+        self.repository.put(b'00000000000000000000000000000000', b'foo')
+        self.repository.commit()
+        self.repository.close()
+        # replace
+        self.repository = self.open()
+        self.repository.put(b'00000000000000000000000000000000', b'bar')
+        self.repository.commit()
+        self.repository.close()
+        # delete
+        self.repository = self.open()
+        self.repository.delete(b'00000000000000000000000000000000')
+        self.repository.commit()
+
+
+
+def suite():
+    return unittest.TestLoader().loadTestsFromTestCase(RepositoryTestCase)
+
+if __name__ == '__main__':
+    unittest.main()