diff --git a/vendor/go.etcd.io/etcd/raft/storage.go b/vendor/go.etcd.io/etcd/raft/storage.go
new file mode 100644
index 0000000..6be5745
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/raft/storage.go
@@ -0,0 +1,273 @@
+// Copyright 2015 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package raft
+
+import (
+	"errors"
+	"sync"
+
+	pb "go.etcd.io/etcd/raft/raftpb"
+)
+
+// ErrCompacted is returned by Storage.Entries/Compact when a requested
+// index is unavailable because it predates the last snapshot.
+var ErrCompacted = errors.New("requested index is unavailable due to compaction")
+
+// ErrSnapOutOfDate is returned by Storage.CreateSnapshot when a requested
+// index is older than the existing snapshot.
+var ErrSnapOutOfDate = errors.New("requested index is older than the existing snapshot")
+
+// ErrUnavailable is returned by Storage interface when the requested log entries
+// are unavailable.
+var ErrUnavailable = errors.New("requested entry at index is unavailable")
+
+// ErrSnapshotTemporarilyUnavailable is returned by the Storage interface when the required
+// snapshot is temporarily unavailable.
+var ErrSnapshotTemporarilyUnavailable = errors.New("snapshot is temporarily unavailable")
+
+// Storage is an interface that may be implemented by the application
+// to retrieve log entries from storage.
+//
+// If any Storage method returns an error, the raft instance will
+// become inoperable and refuse to participate in elections; the
+// application is responsible for cleanup and recovery in this case.
+type Storage interface {
+	// TODO(tbg): split this into two interfaces, LogStorage and StateStorage.
+
+	// InitialState returns the saved HardState and ConfState information.
+	InitialState() (pb.HardState, pb.ConfState, error)
+	// Entries returns a slice of log entries in the range [lo,hi).
+	// MaxSize limits the total size of the log entries returned, but
+	// Entries returns at least one entry if any.
+	Entries(lo, hi, maxSize uint64) ([]pb.Entry, error)
+	// Term returns the term of entry i, which must be in the range
+	// [FirstIndex()-1, LastIndex()]. The term of the entry before
+	// FirstIndex is retained for matching purposes even though the
+	// rest of that entry may not be available.
+	Term(i uint64) (uint64, error)
+	// LastIndex returns the index of the last entry in the log.
+	LastIndex() (uint64, error)
+	// FirstIndex returns the index of the first log entry that is
+	// possibly available via Entries (older entries have been incorporated
+	// into the latest Snapshot; if storage only contains the dummy entry the
+	// first log entry is not available).
+	FirstIndex() (uint64, error)
+	// Snapshot returns the most recent snapshot.
+	// If snapshot is temporarily unavailable, it should return ErrSnapshotTemporarilyUnavailable,
+	// so raft state machine could know that Storage needs some time to prepare
+	// snapshot and call Snapshot later.
+	Snapshot() (pb.Snapshot, error)
+}
+
+// MemoryStorage implements the Storage interface backed by an
+// in-memory array.
+type MemoryStorage struct {
+	// Protects access to all fields. Most methods of MemoryStorage are
+	// run on the raft goroutine, but Append() is run on an application
+	// goroutine.
+	sync.Mutex
+
+	hardState pb.HardState
+	snapshot  pb.Snapshot
+	// ents[i] has raft log position i+snapshot.Metadata.Index
+	ents []pb.Entry
+}
+
+// NewMemoryStorage creates an empty MemoryStorage.
+func NewMemoryStorage() *MemoryStorage {
+	return &MemoryStorage{
+		// When starting from scratch populate the list with a dummy entry at term zero.
+		ents: make([]pb.Entry, 1),
+	}
+}
+
+// InitialState implements the Storage interface.
+func (ms *MemoryStorage) InitialState() (pb.HardState, pb.ConfState, error) {
+	return ms.hardState, ms.snapshot.Metadata.ConfState, nil
+}
+
+// SetHardState saves the current HardState.
+func (ms *MemoryStorage) SetHardState(st pb.HardState) error {
+	ms.Lock()
+	defer ms.Unlock()
+	ms.hardState = st
+	return nil
+}
+
+// Entries implements the Storage interface.
+func (ms *MemoryStorage) Entries(lo, hi, maxSize uint64) ([]pb.Entry, error) {
+	ms.Lock()
+	defer ms.Unlock()
+	offset := ms.ents[0].Index
+	if lo <= offset {
+		return nil, ErrCompacted
+	}
+	if hi > ms.lastIndex()+1 {
+		raftLogger.Panicf("entries' hi(%d) is out of bound lastindex(%d)", hi, ms.lastIndex())
+	}
+	// only contains dummy entries.
+	if len(ms.ents) == 1 {
+		return nil, ErrUnavailable
+	}
+
+	ents := ms.ents[lo-offset : hi-offset]
+	return limitSize(ents, maxSize), nil
+}
+
+// Term implements the Storage interface.
+func (ms *MemoryStorage) Term(i uint64) (uint64, error) {
+	ms.Lock()
+	defer ms.Unlock()
+	offset := ms.ents[0].Index
+	if i < offset {
+		return 0, ErrCompacted
+	}
+	if int(i-offset) >= len(ms.ents) {
+		return 0, ErrUnavailable
+	}
+	return ms.ents[i-offset].Term, nil
+}
+
+// LastIndex implements the Storage interface.
+func (ms *MemoryStorage) LastIndex() (uint64, error) {
+	ms.Lock()
+	defer ms.Unlock()
+	return ms.lastIndex(), nil
+}
+
+func (ms *MemoryStorage) lastIndex() uint64 {
+	return ms.ents[0].Index + uint64(len(ms.ents)) - 1
+}
+
+// FirstIndex implements the Storage interface.
+func (ms *MemoryStorage) FirstIndex() (uint64, error) {
+	ms.Lock()
+	defer ms.Unlock()
+	return ms.firstIndex(), nil
+}
+
+func (ms *MemoryStorage) firstIndex() uint64 {
+	return ms.ents[0].Index + 1
+}
+
+// Snapshot implements the Storage interface.
+func (ms *MemoryStorage) Snapshot() (pb.Snapshot, error) {
+	ms.Lock()
+	defer ms.Unlock()
+	return ms.snapshot, nil
+}
+
+// ApplySnapshot overwrites the contents of this Storage object with
+// those of the given snapshot.
+func (ms *MemoryStorage) ApplySnapshot(snap pb.Snapshot) error {
+	ms.Lock()
+	defer ms.Unlock()
+
+	//handle check for old snapshot being applied
+	msIndex := ms.snapshot.Metadata.Index
+	snapIndex := snap.Metadata.Index
+	if msIndex >= snapIndex {
+		return ErrSnapOutOfDate
+	}
+
+	ms.snapshot = snap
+	ms.ents = []pb.Entry{{Term: snap.Metadata.Term, Index: snap.Metadata.Index}}
+	return nil
+}
+
+// CreateSnapshot makes a snapshot which can be retrieved with Snapshot() and
+// can be used to reconstruct the state at that point.
+// If any configuration changes have been made since the last compaction,
+// the result of the last ApplyConfChange must be passed in.
+func (ms *MemoryStorage) CreateSnapshot(i uint64, cs *pb.ConfState, data []byte) (pb.Snapshot, error) {
+	ms.Lock()
+	defer ms.Unlock()
+	if i <= ms.snapshot.Metadata.Index {
+		return pb.Snapshot{}, ErrSnapOutOfDate
+	}
+
+	offset := ms.ents[0].Index
+	if i > ms.lastIndex() {
+		raftLogger.Panicf("snapshot %d is out of bound lastindex(%d)", i, ms.lastIndex())
+	}
+
+	ms.snapshot.Metadata.Index = i
+	ms.snapshot.Metadata.Term = ms.ents[i-offset].Term
+	if cs != nil {
+		ms.snapshot.Metadata.ConfState = *cs
+	}
+	ms.snapshot.Data = data
+	return ms.snapshot, nil
+}
+
+// Compact discards all log entries prior to compactIndex.
+// It is the application's responsibility to not attempt to compact an index
+// greater than raftLog.applied.
+func (ms *MemoryStorage) Compact(compactIndex uint64) error {
+	ms.Lock()
+	defer ms.Unlock()
+	offset := ms.ents[0].Index
+	if compactIndex <= offset {
+		return ErrCompacted
+	}
+	if compactIndex > ms.lastIndex() {
+		raftLogger.Panicf("compact %d is out of bound lastindex(%d)", compactIndex, ms.lastIndex())
+	}
+
+	i := compactIndex - offset
+	ents := make([]pb.Entry, 1, 1+uint64(len(ms.ents))-i)
+	ents[0].Index = ms.ents[i].Index
+	ents[0].Term = ms.ents[i].Term
+	ents = append(ents, ms.ents[i+1:]...)
+	ms.ents = ents
+	return nil
+}
+
+// Append the new entries to storage.
+// TODO (xiangli): ensure the entries are continuous and
+// entries[0].Index > ms.entries[0].Index
+func (ms *MemoryStorage) Append(entries []pb.Entry) error {
+	if len(entries) == 0 {
+		return nil
+	}
+
+	ms.Lock()
+	defer ms.Unlock()
+
+	first := ms.firstIndex()
+	last := entries[0].Index + uint64(len(entries)) - 1
+
+	// shortcut if there is no new entry.
+	if last < first {
+		return nil
+	}
+	// truncate compacted entries
+	if first > entries[0].Index {
+		entries = entries[first-entries[0].Index:]
+	}
+
+	offset := entries[0].Index - ms.ents[0].Index
+	switch {
+	case uint64(len(ms.ents)) > offset:
+		ms.ents = append([]pb.Entry{}, ms.ents[:offset]...)
+		ms.ents = append(ms.ents, entries...)
+	case uint64(len(ms.ents)) == offset:
+		ms.ents = append(ms.ents, entries...)
+	default:
+		raftLogger.Panicf("missing log entry [last: %d, append at: %d]",
+			ms.lastIndex(), entries[0].Index)
+	}
+	return nil
+}