In case that testpmd or l2fwd are selected as VM loopback application, then VSPERF copies sources of these tools into the shared folder. This folder is mounted by QEMU --drive option, which emulates FAT(16) file system. In theory the limit should be about 2GB, but observed error is triggered once directory content exceeds slightly over 500MB (probably related to underlying linux drive geometry).

A content of shared drive should be checked for unnecessary files to spare size.