diff --git a/builder.go b/builder.go
index 63e4162..22fd248 100644
--- a/builder.go
+++ b/builder.go
@@ -153,7 +153,7 @@ func NewBuilder(ctx context.Context, workdir, imgTag, disk string, size int64, o
 	b := &builder{
 		osRelease: osRelease,
 		img:       img,
-		diskRaw:   filepath.Join(workdir, disk+".raw"),
+		diskRaw:   filepath.Join(workdir, disk+".d2vm.raw"),
 		diskOut:   filepath.Join(workdir, disk+"."+format),
 		format:    f,
 		size:      size,
diff --git a/cmd/d2vm/build.go b/cmd/d2vm/build.go
index 06cd361..b44c997 100644
--- a/cmd/d2vm/build.go
+++ b/cmd/d2vm/build.go
@@ -65,7 +65,7 @@ func init() {
 	buildCmd.Flags().StringVarP(&file, "file", "f", "", "Name of the Dockerfile")
 	buildCmd.Flags().StringArrayVar(&buildArgs, "build-arg", nil, "Set build-time variables")
 
-	buildCmd.Flags().StringVarP(&output, "output", "o", output, "The output image, the extension determine the image format. Supported formats: "+strings.Join(d2vm.OutputFormats(), " "))
+	buildCmd.Flags().StringVarP(&output, "output", "o", output, "The output image, the extension determine the image format, raw will be used if none. Supported formats: "+strings.Join(d2vm.OutputFormats(), " "))
 	buildCmd.Flags().StringVarP(&password, "password", "p", "root", "Root user password")
 	buildCmd.Flags().StringVarP(&size, "size", "s", "10G", "The output image size")
 	buildCmd.Flags().BoolVarP(&debug, "debug", "d", false, "Enable Debug output")
diff --git a/cmd/d2vm/convert.go b/cmd/d2vm/convert.go
index 0500d61..9f9e057 100644
--- a/cmd/d2vm/convert.go
+++ b/cmd/d2vm/convert.go
@@ -93,7 +93,7 @@ func parseSize(s string) (int64, error) {
 
 func init() {
 	convertCmd.Flags().BoolVar(&pull, "pull", false, "Always pull docker image")
-	convertCmd.Flags().StringVarP(&output, "output", "o", output, "The output image, the extension determine the image format. Supported formats: "+strings.Join(d2vm.OutputFormats(), " "))
+	convertCmd.Flags().StringVarP(&output, "output", "o", output, "The output image, the extension determine the image format, raw will be used if none. Supported formats: "+strings.Join(d2vm.OutputFormats(), " "))
 	convertCmd.Flags().StringVarP(&password, "password", "p", "root", "The Root user password")
 	convertCmd.Flags().StringVarP(&size, "size", "s", "10G", "The output image size")
 	convertCmd.Flags().BoolVarP(&debug, "debug", "d", false, "Enable Debug output")
diff --git a/convert.go b/convert.go
index d18c9c9..378a734 100644
--- a/convert.go
+++ b/convert.go
@@ -17,13 +17,13 @@ package d2vm
 import (
 	"context"
 	"fmt"
-	"io"
 	"os"
 	"path/filepath"
 	"strings"
 
 	"github.com/google/uuid"
 	"github.com/sirupsen/logrus"
+	"github.com/svenwiltink/sparsecat"
 
 	"go.linka.cloud/d2vm/pkg/docker"
 )
@@ -64,6 +64,9 @@ func Convert(ctx context.Context, img string, size int64, password string, outpu
 
 	logrus.Infof("creating vm image")
 	format := strings.TrimPrefix(filepath.Ext(output), ".")
+	if format == "" {
+		format = "raw"
+	}
 	b, err := NewBuilder(ctx, tmpPath, imgUUID, "", size, r, format)
 	if err != nil {
 		return err
@@ -92,7 +95,7 @@ func MoveFile(sourcePath, destPath string) error {
 		return fmt.Errorf("failed to open dest file: %s", err)
 	}
 	defer outputFile.Close()
-	_, err = io.Copy(outputFile, inputFile)
+	_, err = sparsecat.NewDecoder(sparsecat.NewEncoder(inputFile)).WriteTo(outputFile)
 	inputFile.Close()
 	if err != nil {
 		return fmt.Errorf("failed to write to output file: %s", err)
diff --git a/go.mod b/go.mod
index e82d403..242d11c 100644
--- a/go.mod
+++ b/go.mod
@@ -37,6 +37,7 @@ require (
 	github.com/pkg/errors v0.9.1 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
 	github.com/spf13/pflag v1.0.5 // indirect
+	github.com/svenwiltink/sparsecat v1.0.0 // indirect
 	github.com/vbatts/tar-split v0.11.2 // indirect
 	go.uber.org/atomic v1.7.0 // indirect
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c // indirect
diff --git a/go.sum b/go.sum
index fc832e2..64e566d 100644
--- a/go.sum
+++ b/go.sum
@@ -743,6 +743,8 @@ github.com/stretchr/testify v1.6.1/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/
 github.com/stretchr/testify v1.7.0 h1:nwc3DEeHmmLAfoZucVR881uASk0Mfjw8xYJ99tb5CcY=
 github.com/stretchr/testify v1.7.0/go.mod h1:6Fq8oRcR53rry900zMqJjRRixrwX3KX962/h/Wwjteg=
 github.com/subosito/gotenv v1.2.0/go.mod h1:N0PQaV/YGNqwC0u51sEeR/aUtSLEXKX9iv69rRypqCw=
+github.com/svenwiltink/sparsecat v1.0.0 h1:SBDEIImxhD//8MskqodFR9VcixWKkZAPAW35nmA4vcw=
+github.com/svenwiltink/sparsecat v1.0.0/go.mod h1:TdtvJbeTZcd+3cMQpttW6MJl/iPGZT0GHmckep0hoxU=
 github.com/syndtr/gocapability v0.0.0-20170704070218-db04d3cc01c8/go.mod h1:hkRG7XYTFWNJGYcbNJQlaLq0fg1yr4J4t/NcTQtrfww=
 github.com/syndtr/gocapability v0.0.0-20180916011248-d98352740cb2/go.mod h1:hkRG7XYTFWNJGYcbNJQlaLq0fg1yr4J4t/NcTQtrfww=
 github.com/syndtr/gocapability v0.0.0-20200815063812-42c35b437635/go.mod h1:hkRG7XYTFWNJGYcbNJQlaLq0fg1yr4J4t/NcTQtrfww=
diff --git a/pkg/exec/exec.go b/pkg/exec/exec.go
index 35b33fb..49506fa 100644
--- a/pkg/exec/exec.go
+++ b/pkg/exec/exec.go
@@ -38,6 +38,7 @@ func SetDebug(debug bool) {
 }
 
 func RunStdout(ctx context.Context, c string, args ...string) error {
+	fmt.Printf("\n$ %s %s\n", c, strings.Join(args, " "))
 	cmd := exec.CommandContext(ctx, c, args...)
 	cmd.Stdout = os.Stdout
 	cmd.Stderr = os.Stderr