diff --git a/internal/datamanager/data.go b/internal/datamanager/data.go
index 7c790c6..10de284 100644
--- a/internal/datamanager/data.go
+++ b/internal/datamanager/data.go
@@ -89,7 +89,7 @@ func (d *DataManager) writeData(ctx context.Context, wals []*WalData) error {
 	if err != nil {
 		return err
 	}
-	if err := d.ost.WriteObject(dataStatusPath(dataSequence.String()), bytes.NewReader(dataStatusj), true); err != nil {
+	if err := d.ost.WriteObject(dataStatusPath(dataSequence.String()), bytes.NewReader(dataStatusj), -1, true); err != nil {
 		return err
 	}
 
@@ -203,7 +203,7 @@ func (d *DataManager) writeDataType(ctx context.Context, wals []*WalData, dataty
 
 		pos += len(dataEntryj)
 	}
-	if err := d.ost.WriteObject(dataFilePath(datatype, dataSequence), &buf, true); err != nil {
+	if err := d.ost.WriteObject(dataFilePath(datatype, dataSequence), &buf, -1, true); err != nil {
 		return err
 	}
 
@@ -211,7 +211,7 @@ func (d *DataManager) writeDataType(ctx context.Context, wals []*WalData, dataty
 	if err != nil {
 		return err
 	}
-	if err := d.ost.WriteObject(dataFileIndexPath(datatype, dataSequence), bytes.NewReader(dataFileIndexj), true); err != nil {
+	if err := d.ost.WriteObject(dataFileIndexPath(datatype, dataSequence), bytes.NewReader(dataFileIndexj), -1, true); err != nil {
 		return err
 	}
 
diff --git a/internal/datamanager/wal.go b/internal/datamanager/wal.go
index 1290cba..0adfba2 100644
--- a/internal/datamanager/wal.go
+++ b/internal/datamanager/wal.go
@@ -485,7 +485,7 @@ func (d *DataManager) WriteWalAdditionalOps(ctx context.Context, actions []*Acti
 			return nil, err
 		}
 	}
-	if err := d.ost.WriteObject(walDataFilePath, bytes.NewReader(buf.Bytes()), true); err != nil {
+	if err := d.ost.WriteObject(walDataFilePath, bytes.NewReader(buf.Bytes()), -1, true); err != nil {
 		return nil, err
 	}
 	d.log.Debugf("wrote wal file: %s", walDataFilePath)
@@ -629,7 +629,7 @@ func (d *DataManager) sync(ctx context.Context) error {
 			}
 
 			walFileCommittedPath := walFilePath + ".committed"
-			if err := d.ost.WriteObject(walFileCommittedPath, bytes.NewReader(headerj), true); err != nil {
+			if err := d.ost.WriteObject(walFileCommittedPath, bytes.NewReader(headerj), -1, true); err != nil {
 				return err
 			}
 
@@ -659,7 +659,7 @@ func (d *DataManager) sync(ctx context.Context) error {
 			walFilePath := d.storageWalStatusFile(walData.WalSequence)
 			d.log.Debugf("checkpointing committed wal to storage")
 			walFileCheckpointedPath := walFilePath + ".checkpointed"
-			if err := d.ost.WriteObject(walFileCheckpointedPath, bytes.NewReader([]byte{}), true); err != nil {
+			if err := d.ost.WriteObject(walFileCheckpointedPath, bytes.NewReader([]byte{}), -1, true); err != nil {
 				return err
 			}
 		}
diff --git a/internal/objectstorage/objectstorage.go b/internal/objectstorage/objectstorage.go
index eb5c996..1555a1d 100644
--- a/internal/objectstorage/objectstorage.go
+++ b/internal/objectstorage/objectstorage.go
@@ -35,7 +35,7 @@ type ReadSeekCloser interface {
 type Storage interface {
 	Stat(filepath string) (*ObjectInfo, error)
 	ReadObject(filepath string) (ReadSeekCloser, error)
-	WriteObject(filepath string, data io.Reader, persist bool) error
+	WriteObject(filepath string, data io.Reader, size int64, persist bool) error
 	DeleteObject(filepath string) error
 	List(prefix, startWith, delimiter string, doneCh <-chan struct{}) <-chan ObjectInfo
 }
diff --git a/internal/objectstorage/objectstorage_test.go b/internal/objectstorage/objectstorage_test.go
index 667d7e2..c008da2 100644
--- a/internal/objectstorage/objectstorage_test.go
+++ b/internal/objectstorage/objectstorage_test.go
@@ -260,7 +260,7 @@ func TestList(t *testing.T) {
 				os := NewObjStorage(s, "/")
 				// populate
 				for _, p := range tt.objects {
-					if err := os.WriteObject(p, strings.NewReader(""), true); err != nil {
+					if err := os.WriteObject(p, strings.NewReader(""), 0, true); err != nil {
 						t.Fatalf("%s %d err: %v", sname, i, err)
 					}
 				}
diff --git a/internal/objectstorage/posix.go b/internal/objectstorage/posix.go
index 5a3e5ff..75a687b 100644
--- a/internal/objectstorage/posix.go
+++ b/internal/objectstorage/posix.go
@@ -264,7 +264,7 @@ func (s *PosixStorage) ReadObject(p string) (ReadSeekCloser, error) {
 	return f, err
 }
 
-func (s *PosixStorage) WriteObject(p string, data io.Reader, persist bool) error {
+func (s *PosixStorage) WriteObject(p string, data io.Reader, size int64, persist bool) error {
 	fspath, err := s.fsPath(p)
 	if err != nil {
 		return err
diff --git a/internal/objectstorage/posix_test.go b/internal/objectstorage/posix_test.go
index 7787532..35f1255 100644
--- a/internal/objectstorage/posix_test.go
+++ b/internal/objectstorage/posix_test.go
@@ -92,7 +92,7 @@ func TestDeleteObject(t *testing.T) {
 	}
 
 	for _, obj := range objects {
-		if err := ls.WriteObject(obj, bytes.NewReader([]byte{}), true); err != nil {
+		if err := ls.WriteObject(obj, bytes.NewReader([]byte{}), 0, true); err != nil {
 			t.Fatalf("unexpected err: %v", err)
 		}
 		if err := ls.DeleteObject(obj); err != nil {
diff --git a/internal/objectstorage/s3.go b/internal/objectstorage/s3.go
index 303acf8..b94ba23 100644
--- a/internal/objectstorage/s3.go
+++ b/internal/objectstorage/s3.go
@@ -84,16 +84,25 @@ func (s *S3Storage) ReadObject(filepath string) (ReadSeekCloser, error) {
 	return s.minioClient.GetObject(s.bucket, filepath, minio.GetObjectOptions{})
 }
 
-func (s *S3Storage) WriteObject(filepath string, data io.Reader, persist bool) error {
+func (s *S3Storage) WriteObject(filepath string, data io.Reader, size int64, persist bool) error {
+	// if size is not specified, limit max object size to defaultMaxObjectSize so
+	// minio client will not calculate a very big part size using tons of ram.
+	// An alternative is to write the file locally so we can calculate the size and
+	// then put it. See commented out code below.
+	if size >= 0 {
+		_, err := s.minioClient.PutObject(s.bucket, filepath, data, size, minio.PutObjectOptions{ContentType: "application/octet-stream"})
+		return err
+	}
+
 	// hack to know the real file size or minio will do this in memory with big memory usage since s3 doesn't support real streaming of unknown sizes
-	// TODO(sgotti) wait for minio client to expose an api to provide the max part size so we can remove this
+	// TODO(sgotti) wait for minio client to expose an api to provide the max object size so we can remove this
 	tmpfile, err := ioutil.TempFile(os.TempDir(), "s3")
 	if err != nil {
 		return err
 	}
 	defer tmpfile.Close()
 	defer os.Remove(tmpfile.Name())
-	size, err := io.Copy(tmpfile, data)
+	size, err = io.Copy(tmpfile, data)
 	if err != nil {
 		return err
 	}
diff --git a/internal/services/runservice/scheduler/api/executor.go b/internal/services/runservice/scheduler/api/executor.go
index deab9ab..43d41f3 100644
--- a/internal/services/runservice/scheduler/api/executor.go
+++ b/internal/services/runservice/scheduler/api/executor.go
@@ -411,7 +411,7 @@ func (h *CacheCreateHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	cachePath := store.OSTCachePath(key)
-	if err := h.ost.WriteObject(cachePath, r.Body, false); err != nil {
+	if err := h.ost.WriteObject(cachePath, r.Body, -1, false); err != nil {
 		http.Error(w, err.Error(), http.StatusInternalServerError)
 		return
 	}
diff --git a/internal/services/runservice/scheduler/scheduler.go b/internal/services/runservice/scheduler/scheduler.go
index 0ad45b5..d8dfa43 100644
--- a/internal/services/runservice/scheduler/scheduler.go
+++ b/internal/services/runservice/scheduler/scheduler.go
@@ -931,7 +931,7 @@ func (s *Scheduler) fetchLog(ctx context.Context, rt *types.RunTask, setup bool,
 		return errors.Errorf("received http status: %d", r.StatusCode)
 	}
 
-	return s.ost.WriteObject(logPath, r.Body, false)
+	return s.ost.WriteObject(logPath, r.Body, -1, false)
 }
 
 func (s *Scheduler) finishSetupLogPhase(ctx context.Context, runID, runTaskID string) error {
@@ -1073,7 +1073,7 @@ func (s *Scheduler) fetchArchive(ctx context.Context, rt *types.RunTask, stepnum
 		return errors.Errorf("received http status: %d", r.StatusCode)
 	}
 
-	return s.ost.WriteObject(path, r.Body, false)
+	return s.ost.WriteObject(path, r.Body, -1, false)
 }
 
 func (s *Scheduler) fetchTaskArchives(ctx context.Context, runID string, rt *types.RunTask) {