diff --git a/tests/qemu-iotests/179 b/tests/qemu-iotests/179
new file mode 100755
index 0000000000..7bc8db8fe0
--- /dev/null
+++ b/tests/qemu-iotests/179
@@ -0,0 +1,130 @@
+#!/bin/bash
+#
+# Test case for write zeroes with unmap
+#
+# Copyright (C) 2017 Red Hat, Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see .
+#
+
+# creator
+owner=eblake@redhat.com
+
+seq="$(basename $0)"
+echo "QA output created by $seq"
+
+here="$PWD"
+status=1 # failure is the default!
+
+_cleanup()
+{
+ _cleanup_test_img
+}
+trap "_cleanup; exit \$status" 0 1 2 3 15
+
+# get standard environment, filters and checks
+. ./common.rc
+. ./common.filter
+
+_supported_fmt qcow2
+_supported_proto file
+_supported_os Linux
+
+# v2 images can't mark clusters as zero
+_unsupported_imgopts compat=0.10
+
+echo
+echo '=== Testing write zeroes with unmap ==='
+echo
+
+TEST_IMG="$TEST_IMG.base" _make_test_img 64M
+_make_test_img -b "$TEST_IMG.base"
+
+# Offsets chosen at or near 2M boundaries so test works at all cluster sizes
+# 8k and larger (smaller clusters fail due to non-contiguous allocations)
+
+# Aligned writes to unallocated cluster should not allocate mapping, but must
+# mark cluster as zero, whether or not unmap was requested
+$QEMU_IO -c "write -z -u 2M 2M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "write -z 6M 2M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "map" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IMG map --output=json "$TEST_IMG.base" | _filter_qemu_img_map
+
+# Unaligned writes need not allocate mapping if the cluster already reads
+# as zero, but must mark cluster as zero, whether or not unmap was requested
+$QEMU_IO -c "write -z -u 10485761 2097150" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "write -z 14680065 2097150" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "map" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IMG map --output=json "$TEST_IMG.base" | _filter_qemu_img_map
+
+# Requesting unmap of normal data must deallocate; omitting unmap should
+# preserve the mapping
+$QEMU_IO -c "write 18M 14M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "write -z -u 20M 2M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "write -z 24M 6M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "map" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IMG map --output=json "$TEST_IMG.base" | _filter_qemu_img_map
+
+# Likewise when writing on already-mapped zero data
+$QEMU_IO -c "write -z -u 26M 2M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "write -z 28M 2M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "map" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IMG map --output=json "$TEST_IMG.base" | _filter_qemu_img_map
+
+# Writing on unmapped zeroes does not allocate
+$QEMU_IO -c "write -z 32M 8M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "write -z -u 34M 2M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "write -z 36M 2M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "map" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IMG map --output=json "$TEST_IMG.base" | _filter_qemu_img_map
+
+# Writing zero overrides a backing file, regardless of backing cluster type
+$QEMU_IO -c "write -z 40M 8M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "write 48M 8M" "$TEST_IMG.base" | _filter_qemu_io
+$QEMU_IO -c "write -z -u 42M 2M" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "write -z 44M 2M" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "write -z -u 50M 2M" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "write -z 52M 2M" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "write -z -u 58M 2M" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "write -z 60M 2M" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IO -c "map" "$TEST_IMG" | _filter_qemu_io
+$QEMU_IMG map --output=json "$TEST_IMG" | _filter_qemu_img_map
+
+# Final check that mappings are correct and images are still sane
+TEST_IMG="$TEST_IMG.base" _check_test_img
+_check_test_img
+
+echo
+echo '=== Testing cache optimization ==='
+echo
+
+BLKDBG_TEST_IMG="blkdebug:$TEST_DIR/blkdebug.conf:$TEST_IMG.base"
+
+cat > "$TEST_DIR/blkdebug.conf" <