diff --git a/src/driver/tpax_driver_ctx.c b/src/driver/tpax_driver_ctx.c
index 1498718..30f3ce5 100644
--- a/src/driver/tpax_driver_ctx.c
+++ b/src/driver/tpax_driver_ctx.c
@@ -283,7 +283,7 @@ static struct tpax_driver_ctx_impl * tpax_driver_ctx_alloc(
 			*units++ = entry->arg;
 
 	if (cctx->drvflags & TPAX_DRIVER_EXEC_MODE_WRITE_COPY) {
-		ictx->ctx.bufsize = 64 * 1024;
+		ictx->ctx.bufsize = TPAX_FILEIO_BUFLEN;
 		ictx->ctx.bufaddr = mmap(
 			0,ictx->ctx.bufsize,
 			PROT_READ|PROT_WRITE,
diff --git a/src/internal/tpax_driver_impl.h b/src/internal/tpax_driver_impl.h
index 47d8fd5..9396d19 100644
--- a/src/internal/tpax_driver_impl.h
+++ b/src/internal/tpax_driver_impl.h
@@ -20,6 +20,7 @@
 
 #define TPAX_OPTV_ELEMENTS 64
 #define TPAX_DIRENT_BUFLEN 65536
+#define TPAX_FILEIO_BUFLEN (4096 * 1024)
 
 #define TPAX_DRIVER_EXEC_MODE_WRITE_COPY \
 	(TPAX_DRIVER_EXEC_MODE_WRITE |    \