diff --git a/job.go b/job.go
index 17b922e..8f8331f 100644
--- a/job.go
+++ b/job.go
@@ -126,9 +126,30 @@ type writeJob struct {
 	ch  chan struct{}
 }
 
+func newWriteJob(job *baseJob, src *mmap.ReaderAt, needWait bool) *writeJob {
+	j := &writeJob{
+		baseJob: job,
+		src:     src,
+	}
+	if needWait {
+		j.ch = make(chan struct{})
+	}
+	return j
+}
+
 func (wj *writeJob) done() {
 	wj.src.Close()
-	close(wj.ch)
+
+	if wj.ch != nil {
+		close(wj.ch)
+	}
+}
+
+func (wj *writeJob) wait() {
+	if wj.ch == nil {
+		return
+	}
+	<-wj.ch
 }
 
 type Job struct {
diff --git a/opt.go b/opt.go
index e58e4cc..f6aaeb9 100644
--- a/opt.go
+++ b/opt.go
@@ -91,6 +91,10 @@ func (o *option) check() error {
 
 	o.fromDevice.check()
 	o.toDevice.check()
+	if o.fromDevice.linear || o.toDevice.linear {
+		o.fromDevice.threads = 1
+		o.toDevice.threads = 1
+	}
 	if o.logger == nil {
 		o.logger = logrus.StandardLogger()
 	}
diff --git a/prepare.go b/prepare.go
index b4f891d..ff2aee7 100644
--- a/prepare.go
+++ b/prepare.go
@@ -45,9 +45,9 @@ func (c *Copyer) prepare(ctx context.Context, indexed <-chan *baseJob) <-chan *w
 						return
 					}
 
-					wj := &writeJob{baseJob: job, src: file, ch: make(chan struct{})}
+					wj := newWriteJob(job, file, c.fromDevice.linear)
 					ch <- wj
-					<-wj.ch
+					wj.wait()
 				}
 			}
 		})