diff --git a/endpoint/endpoint.go b/endpoint/endpoint.go
index 55c41c5..8a26730 100644
--- a/endpoint/endpoint.go
+++ b/endpoint/endpoint.go
@@ -75,16 +75,19 @@ func (p *Sender) Send(ctx context.Context, r *pdu.SendReq) (*pdu.SendRes, io.Rea
 		return nil, nil, replication.NewFilteredError(r.Filesystem)
 	}
 
-	size, err := zfs.ZFSSendDry(r.Filesystem, r.From, r.To)
-	if err != nil {
-		return nil, nil, err
+	if r.DryRun {
+		size, err := zfs.ZFSSendDry(r.Filesystem, r.From, r.To)
+		if err != nil {
+			return nil, nil, err
+		}
+		return &pdu.SendRes{ExpectedSize: size}, nil, nil
+	} else {
+		stream, err := zfs.ZFSSend(r.Filesystem, r.From, r.To)
+		if err != nil {
+			return nil, nil, err
+		}
+		return &pdu.SendRes{}, stream, nil
 	}
-
-	stream, err := zfs.ZFSSend(r.Filesystem, r.From, r.To)
-	if err != nil {
-		return nil, nil, err
-	}
-	return &pdu.SendRes{ExpectedSize: size}, stream, nil
 }
 
 func (p *Sender) DestroySnapshots(ctx context.Context, req *pdu.DestroySnapshotsReq) (*pdu.DestroySnapshotsRes, error) {
diff --git a/replication/fsrep/fsfsm.go b/replication/fsrep/fsfsm.go
index 43bbf59..2462cba 100644
--- a/replication/fsrep/fsfsm.go
+++ b/replication/fsrep/fsfsm.go
@@ -40,7 +40,7 @@ func getLogger(ctx context.Context) Logger {
 type Sender interface {
 	// If a non-nil io.ReadCloser is returned, it is guaranteed to be closed before
 	// any next call to the parent github.com/zrepl/zrepl/replication.Endpoint.
-	// returned int64 is the expected size of the stream
+	// If the send request is for dry run the io.ReadCloser will be nil
 	Send(ctx context.Context, r *pdu.SendReq) (*pdu.SendRes, io.ReadCloser, error)
 	SnapshotReplicationStatus(ctx context.Context, r *pdu.SnapshotReplicationStatusReq) (*pdu.SnapshotReplicationStatusRes, error)
 }
@@ -105,6 +105,17 @@ func (f *Replication) State() State {
 	return f.state
 }
 
+func (f *Replication) UpdateSizeEsitmate(ctx context.Context, sender Sender) error {
+	f.lock.Lock()
+	defer f.lock.Unlock()
+	for _, e := range f.pending {
+		if err := e.updateSizeEstimate(ctx, sender); err != nil {
+			return err
+		}
+	}
+	return nil
+}
+
 type ReplicationBuilder struct {
 	r *Replication
 }
@@ -344,19 +355,7 @@ func (s *ReplicationStep) doReplication(ctx context.Context, sender Sender, rece
 		return s.state
 	}
 
-	var sr *pdu.SendReq
-	if s.from == nil {
-		sr = &pdu.SendReq{
-			Filesystem: fs,
-			From:       s.to.RelName(), // FIXME fix protocol to use To, like zfs does internally
-		}
-	} else {
-		sr = &pdu.SendReq{
-			Filesystem: fs,
-			From:       s.from.RelName(),
-			To:         s.to.RelName(),
-		}
-	}
+	sr := s.buildSendRequest(false)
 
 	log.WithField("request", sr).Debug("initiate send request")
 	sres, sstream, err := sender.Send(ctx, sr)
@@ -369,7 +368,6 @@ func (s *ReplicationStep) doReplication(ctx context.Context, sender Sender, rece
 		return updateStateError(err)
 	}
 
-	s.expectedSize = sres.ExpectedSize
 	s.byteCounter = util.NewByteCounterReader(sstream)
 	sstream = s.byteCounter
 
@@ -442,6 +440,44 @@ func (s *ReplicationStep) doMarkReplicated(ctx context.Context, sender Sender) S
 	return updateStateCompleted()
 }
 
+func (s *ReplicationStep) updateSizeEstimate(ctx context.Context, sender Sender) error {
+
+	fs := s.parent.fs
+
+	log := getLogger(ctx).
+		WithField("filesystem", fs).
+		WithField("step", s.String())
+
+	sr := s.buildSendRequest(true)
+
+	log.WithField("request", sr).Debug("initiate dry run send request")
+	sres, _, err := sender.Send(ctx, sr)
+	if err != nil {
+		log.WithError(err).Error("dry run send request failed")
+	}
+	s.expectedSize = sres.ExpectedSize
+	return nil
+}
+
+func (s *ReplicationStep) buildSendRequest(dryRun bool) (sr *pdu.SendReq) {
+	fs := s.parent.fs
+	if s.from == nil {
+		sr = &pdu.SendReq{
+			Filesystem: fs,
+			From:       s.to.RelName(), // FIXME fix protocol to use To, like zfs does internally
+			DryRun:     dryRun,
+		}
+	} else {
+		sr = &pdu.SendReq{
+			Filesystem: fs,
+			From:       s.from.RelName(),
+			To:         s.to.RelName(),
+			DryRun:     dryRun,
+		}
+	}
+	return sr
+}
+
 func (s *ReplicationStep) String() string {
 	if s.from == nil { // FIXME: ZFS semantics are that to is nil on non-incremental send
 		return fmt.Sprintf("%s%s (full)", s.parent.fs, s.to.RelName())
diff --git a/replication/mainfsm.go b/replication/mainfsm.go
index 2fc5cc3..d30f417 100644
--- a/replication/mainfsm.go
+++ b/replication/mainfsm.go
@@ -266,6 +266,10 @@ func statePlanning(ctx context.Context, sender Sender, receiver Receiver, u upda
 			}
 		}
 		qitem := fsrfsm.Done()
+		if err = qitem.UpdateSizeEsitmate(ctx, sender); err != nil {
+			log.WithError(err).Error("cannot get size estimate")
+			return handlePlanningError(err)
+		}
 		q.Add(qitem)
 	}
 
diff --git a/replication/pdu/pdu.pb.go b/replication/pdu/pdu.pb.go
index 3ca7077..a1876f8 100644
--- a/replication/pdu/pdu.pb.go
+++ b/replication/pdu/pdu.pb.go
@@ -38,7 +38,7 @@ func (x FilesystemVersion_VersionType) String() string {
 	return proto.EnumName(FilesystemVersion_VersionType_name, int32(x))
 }
 func (FilesystemVersion_VersionType) EnumDescriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{5, 0}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{5, 0}
 }
 
 type SnapshotReplicationStatusReq_Op int32
@@ -61,7 +61,7 @@ func (x SnapshotReplicationStatusReq_Op) String() string {
 	return proto.EnumName(SnapshotReplicationStatusReq_Op_name, int32(x))
 }
 func (SnapshotReplicationStatusReq_Op) EnumDescriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{14, 0}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{14, 0}
 }
 
 type ListFilesystemReq struct {
@@ -74,7 +74,7 @@ func (m *ListFilesystemReq) Reset()         { *m = ListFilesystemReq{} }
 func (m *ListFilesystemReq) String() string { return proto.CompactTextString(m) }
 func (*ListFilesystemReq) ProtoMessage()    {}
 func (*ListFilesystemReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{0}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{0}
 }
 func (m *ListFilesystemReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ListFilesystemReq.Unmarshal(m, b)
@@ -105,7 +105,7 @@ func (m *ListFilesystemRes) Reset()         { *m = ListFilesystemRes{} }
 func (m *ListFilesystemRes) String() string { return proto.CompactTextString(m) }
 func (*ListFilesystemRes) ProtoMessage()    {}
 func (*ListFilesystemRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{1}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{1}
 }
 func (m *ListFilesystemRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ListFilesystemRes.Unmarshal(m, b)
@@ -144,7 +144,7 @@ func (m *Filesystem) Reset()         { *m = Filesystem{} }
 func (m *Filesystem) String() string { return proto.CompactTextString(m) }
 func (*Filesystem) ProtoMessage()    {}
 func (*Filesystem) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{2}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{2}
 }
 func (m *Filesystem) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Filesystem.Unmarshal(m, b)
@@ -189,7 +189,7 @@ func (m *ListFilesystemVersionsReq) Reset()         { *m = ListFilesystemVersion
 func (m *ListFilesystemVersionsReq) String() string { return proto.CompactTextString(m) }
 func (*ListFilesystemVersionsReq) ProtoMessage()    {}
 func (*ListFilesystemVersionsReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{3}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{3}
 }
 func (m *ListFilesystemVersionsReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ListFilesystemVersionsReq.Unmarshal(m, b)
@@ -227,7 +227,7 @@ func (m *ListFilesystemVersionsRes) Reset()         { *m = ListFilesystemVersion
 func (m *ListFilesystemVersionsRes) String() string { return proto.CompactTextString(m) }
 func (*ListFilesystemVersionsRes) ProtoMessage()    {}
 func (*ListFilesystemVersionsRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{4}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{4}
 }
 func (m *ListFilesystemVersionsRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ListFilesystemVersionsRes.Unmarshal(m, b)
@@ -269,7 +269,7 @@ func (m *FilesystemVersion) Reset()         { *m = FilesystemVersion{} }
 func (m *FilesystemVersion) String() string { return proto.CompactTextString(m) }
 func (*FilesystemVersion) ProtoMessage()    {}
 func (*FilesystemVersion) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{5}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{5}
 }
 func (m *FilesystemVersion) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_FilesystemVersion.Unmarshal(m, b)
@@ -339,6 +339,7 @@ type SendReq struct {
 	ResumeToken          string   `protobuf:"bytes,4,opt,name=ResumeToken,proto3" json:"ResumeToken,omitempty"`
 	Compress             bool     `protobuf:"varint,5,opt,name=Compress,proto3" json:"Compress,omitempty"`
 	Dedup                bool     `protobuf:"varint,6,opt,name=Dedup,proto3" json:"Dedup,omitempty"`
+	DryRun               bool     `protobuf:"varint,7,opt,name=DryRun,proto3" json:"DryRun,omitempty"`
 	XXX_NoUnkeyedLiteral struct{} `json:"-"`
 	XXX_unrecognized     []byte   `json:"-"`
 	XXX_sizecache        int32    `json:"-"`
@@ -348,7 +349,7 @@ func (m *SendReq) Reset()         { *m = SendReq{} }
 func (m *SendReq) String() string { return proto.CompactTextString(m) }
 func (*SendReq) ProtoMessage()    {}
 func (*SendReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{6}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{6}
 }
 func (m *SendReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_SendReq.Unmarshal(m, b)
@@ -410,6 +411,13 @@ func (m *SendReq) GetDedup() bool {
 	return false
 }
 
+func (m *SendReq) GetDryRun() bool {
+	if m != nil {
+		return m.DryRun
+	}
+	return false
+}
+
 type Property struct {
 	Name                 string   `protobuf:"bytes,1,opt,name=Name,proto3" json:"Name,omitempty"`
 	Value                string   `protobuf:"bytes,2,opt,name=Value,proto3" json:"Value,omitempty"`
@@ -422,7 +430,7 @@ func (m *Property) Reset()         { *m = Property{} }
 func (m *Property) String() string { return proto.CompactTextString(m) }
 func (*Property) ProtoMessage()    {}
 func (*Property) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{7}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{7}
 }
 func (m *Property) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_Property.Unmarshal(m, b)
@@ -471,7 +479,7 @@ func (m *SendRes) Reset()         { *m = SendRes{} }
 func (m *SendRes) String() string { return proto.CompactTextString(m) }
 func (*SendRes) ProtoMessage()    {}
 func (*SendRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{8}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{8}
 }
 func (m *SendRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_SendRes.Unmarshal(m, b)
@@ -525,7 +533,7 @@ func (m *ReceiveReq) Reset()         { *m = ReceiveReq{} }
 func (m *ReceiveReq) String() string { return proto.CompactTextString(m) }
 func (*ReceiveReq) ProtoMessage()    {}
 func (*ReceiveReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{9}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{9}
 }
 func (m *ReceiveReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ReceiveReq.Unmarshal(m, b)
@@ -569,7 +577,7 @@ func (m *ReceiveRes) Reset()         { *m = ReceiveRes{} }
 func (m *ReceiveRes) String() string { return proto.CompactTextString(m) }
 func (*ReceiveRes) ProtoMessage()    {}
 func (*ReceiveRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{10}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{10}
 }
 func (m *ReceiveRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_ReceiveRes.Unmarshal(m, b)
@@ -602,7 +610,7 @@ func (m *DestroySnapshotsReq) Reset()         { *m = DestroySnapshotsReq{} }
 func (m *DestroySnapshotsReq) String() string { return proto.CompactTextString(m) }
 func (*DestroySnapshotsReq) ProtoMessage()    {}
 func (*DestroySnapshotsReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{11}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{11}
 }
 func (m *DestroySnapshotsReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_DestroySnapshotsReq.Unmarshal(m, b)
@@ -648,7 +656,7 @@ func (m *DestroySnapshotRes) Reset()         { *m = DestroySnapshotRes{} }
 func (m *DestroySnapshotRes) String() string { return proto.CompactTextString(m) }
 func (*DestroySnapshotRes) ProtoMessage()    {}
 func (*DestroySnapshotRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{12}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{12}
 }
 func (m *DestroySnapshotRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_DestroySnapshotRes.Unmarshal(m, b)
@@ -693,7 +701,7 @@ func (m *DestroySnapshotsRes) Reset()         { *m = DestroySnapshotsRes{} }
 func (m *DestroySnapshotsRes) String() string { return proto.CompactTextString(m) }
 func (*DestroySnapshotsRes) ProtoMessage()    {}
 func (*DestroySnapshotsRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{13}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{13}
 }
 func (m *DestroySnapshotsRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_DestroySnapshotsRes.Unmarshal(m, b)
@@ -733,7 +741,7 @@ func (m *SnapshotReplicationStatusReq) Reset()         { *m = SnapshotReplicatio
 func (m *SnapshotReplicationStatusReq) String() string { return proto.CompactTextString(m) }
 func (*SnapshotReplicationStatusReq) ProtoMessage()    {}
 func (*SnapshotReplicationStatusReq) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{14}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{14}
 }
 func (m *SnapshotReplicationStatusReq) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_SnapshotReplicationStatusReq.Unmarshal(m, b)
@@ -785,7 +793,7 @@ func (m *SnapshotReplicationStatusRes) Reset()         { *m = SnapshotReplicatio
 func (m *SnapshotReplicationStatusRes) String() string { return proto.CompactTextString(m) }
 func (*SnapshotReplicationStatusRes) ProtoMessage()    {}
 func (*SnapshotReplicationStatusRes) Descriptor() ([]byte, []int) {
-	return fileDescriptor_pdu_cc43fc3f9f8b50e6, []int{15}
+	return fileDescriptor_pdu_ae88208ed9690d0f, []int{15}
 }
 func (m *SnapshotReplicationStatusRes) XXX_Unmarshal(b []byte) error {
 	return xxx_messageInfo_SnapshotReplicationStatusRes.Unmarshal(m, b)
@@ -833,47 +841,48 @@ func init() {
 	proto.RegisterEnum("pdu.SnapshotReplicationStatusReq_Op", SnapshotReplicationStatusReq_Op_name, SnapshotReplicationStatusReq_Op_value)
 }
 
-func init() { proto.RegisterFile("pdu.proto", fileDescriptor_pdu_cc43fc3f9f8b50e6) }
+func init() { proto.RegisterFile("pdu.proto", fileDescriptor_pdu_ae88208ed9690d0f) }
 
-var fileDescriptor_pdu_cc43fc3f9f8b50e6 = []byte{
-	// 616 bytes of a gzipped FileDescriptorProto
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+var fileDescriptor_pdu_ae88208ed9690d0f = []byte{
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 }
diff --git a/replication/pdu/pdu.proto b/replication/pdu/pdu.proto
index 2e6f045..211fc0e 100644
--- a/replication/pdu/pdu.proto
+++ b/replication/pdu/pdu.proto
@@ -50,6 +50,8 @@ message SendReq {
     string ResumeToken  = 4;
     bool Compress = 5;
     bool Dedup = 6;
+
+    bool DryRun = 7;
 }
 
 message Property {