diff --git a/fs_mgr/libsnapshot/Android.bp b/fs_mgr/libsnapshot/Android.bp
index 996fbca..e7de84c 100644
--- a/fs_mgr/libsnapshot/Android.bp
+++ b/fs_mgr/libsnapshot/Android.bp
@@ -226,3 +226,19 @@
         "libutils",
     ],
 }
+
+cc_test {
+    name: "snapshot_power_test",
+    srcs: [
+        "power_test.cpp",
+    ],
+    static_libs: [
+        "libsnapshot",
+    ],
+    shared_libs: [
+        "libbase",
+        "libfs_mgr_binder",
+        "liblog",
+    ],
+    gtest: false,
+}
diff --git a/fs_mgr/libsnapshot/PowerTest.md b/fs_mgr/libsnapshot/PowerTest.md
new file mode 100644
index 0000000..0b0cb5d
--- /dev/null
+++ b/fs_mgr/libsnapshot/PowerTest.md
@@ -0,0 +1,40 @@
+snapshot\_power\_test
+---------------------
+
+snapshot\_power\_test is a standalone test to simulate power failures during a snapshot-merge operation.
+
+### Test Setup
+
+Start by creating two large files that will be used as the pre-merge and post-merge state. You can take two different partition images (for example, a product.img from two separate builds), or just create random data:
+
+	dd if=/dev/urandom of=pre-merge count=1024 bs=1048576
+	dd if=/dev/urandom of=post-merge count=1024 bs=1048576
+
+Next, push these files to an unencrypted directory on the device:
+
+	adb push pre-merge /data/local/unencrypted
+	adb push post-merge /data/local/unencrypted
+
+Next, run the test setup:
+
+	adb sync data
+	adb shell /data/nativetest64/snapshot_power_test/snapshot_power_test \
+		/data/local/unencrypted/pre-merge \
+		/data/local/unencrypted/post-merge
+
+This will create the necessary fiemap-based images.
+
+### Running
+The actual test can be run via `run_power_test.sh`. Its syntax is:
+
+	run_power_test.sh <POST_MERGE_FILE>
+
+`POST_MERGE_FILE` should be the path on the device of the image to validate the merge against. Example:
+
+	run_power_test.sh /data/local/unencrypted/post-merge
+
+The device will begin the merge with a 5% chance of injecting a kernel crash every 10ms. The device should be capable of rebooting normally without user intervention. Once the merge has completed, the test will run a final check command to validate the contents of the snapshot against the post-merge file. It will error if there are any incorrect blocks.
+
+Two environment variables can be passed to `run_power_test.sh`:
+1. `FAIL_RATE` - A fraction between 0 and 100 (inclusive) indicating the probability the device should inject a kernel crash every 10ms.
+2. `DEVICE_SERIAL` - If multiple devices are attached to adb, this argument is passed as the serial to select (to `adb -s`).
diff --git a/fs_mgr/libsnapshot/power_test.cpp b/fs_mgr/libsnapshot/power_test.cpp
new file mode 100644
index 0000000..4d2548a
--- /dev/null
+++ b/fs_mgr/libsnapshot/power_test.cpp
@@ -0,0 +1,559 @@
+//
+// Copyright (C) 2020 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+#include <errno.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#include <chrono>
+#include <iostream>
+#include <random>
+#include <string>
+#include <thread>
+#include <vector>
+
+#include <android-base/file.h>
+#include <android-base/parsedouble.h>
+#include <android-base/stringprintf.h>
+#include <android-base/strings.h>
+#include <android-base/unique_fd.h>
+#include <ext4_utils/ext4_utils.h>
+#include <fstab/fstab.h>
+#include <libdm/dm.h>
+#include <libfiemap/image_manager.h>
+
+using namespace std::chrono_literals;
+using namespace std::string_literals;
+using android::base::borrowed_fd;
+using android::base::unique_fd;
+using android::dm::DeviceMapper;
+using android::dm::DmDeviceState;
+using android::dm::DmTable;
+using android::dm::DmTargetSnapshot;
+using android::dm::SnapshotStorageMode;
+using android::fiemap::ImageManager;
+using android::fs_mgr::Fstab;
+
+namespace android {
+namespace snapshot {
+
+static void usage() {
+    std::cerr << "Usage:\n";
+    std::cerr << "  create <orig-payload> <new-payload>\n";
+    std::cerr << "\n";
+    std::cerr << "  Create a snapshot device containing the contents of\n";
+    std::cerr << "  orig-payload, and then write the contents of new-payload.\n";
+    std::cerr << "  The original files are not modified.\n";
+    std::cerr << "\n";
+    std::cerr << "  merge <fail-rate>\n";
+    std::cerr << "\n";
+    std::cerr << "  Merge the snapshot previously started by create, and wait\n";
+    std::cerr << "  for it to complete. Once done, it is compared to the\n";
+    std::cerr << "  new-payload for consistency. The original files are not \n";
+    std::cerr << "  modified. If a fail-rate is passed (as a fraction between 0\n";
+    std::cerr << "  and 100), every 10ms the device has that percent change of\n";
+    std::cerr << "  injecting a kernel crash.\n";
+    std::cerr << "\n";
+    std::cerr << "  check <new-payload>\n";
+    std::cerr << "  Verify that all artifacts are correct after a merge\n";
+    std::cerr << "  completes.\n";
+    std::cerr << "\n";
+    std::cerr << "  cleanup\n";
+    std::cerr << "  Remove all ImageManager artifacts from create/merge.\n";
+}
+
+class PowerTest final {
+  public:
+    PowerTest();
+    bool Run(int argc, char** argv);
+
+  private:
+    bool OpenImageManager();
+    bool Create(int argc, char** argv);
+    bool Merge(int argc, char** argv);
+    bool Check(int argc, char** argv);
+    bool Cleanup();
+    bool CleanupImage(const std::string& name);
+    bool SetupImages(const std::string& first_file, borrowed_fd second_fd);
+    bool MapImages();
+    bool MapSnapshot(SnapshotStorageMode mode);
+    bool GetMergeStatus(DmTargetSnapshot::Status* status);
+
+    static constexpr char kSnapshotName[] = "snapshot-power-test";
+    static constexpr char kSnapshotImageName[] = "snapshot-power-test-image";
+    static constexpr char kSnapshotCowName[] = "snapshot-power-test-cow";
+
+    DeviceMapper& dm_;
+    std::unique_ptr<ImageManager> images_;
+    std::string image_path_;
+    std::string cow_path_;
+    std::string snapshot_path_;
+};
+
+PowerTest::PowerTest() : dm_(DeviceMapper::Instance()) {}
+
+bool PowerTest::Run([[maybe_unused]] int argc, [[maybe_unused]] char** argv) {
+    if (!OpenImageManager()) {
+        return false;
+    }
+
+    if (argc < 2) {
+        usage();
+        return false;
+    }
+    if (argv[1] == "create"s) {
+        return Create(argc, argv);
+    } else if (argv[1] == "merge"s) {
+        return Merge(argc, argv);
+    } else if (argv[1] == "check"s) {
+        return Check(argc, argv);
+    } else if (argv[1] == "cleanup"s) {
+        return Cleanup();
+    } else {
+        usage();
+        return false;
+    }
+}
+
+bool PowerTest::OpenImageManager() {
+    std::vector<std::string> dirs = {
+            "/data/gsi/test",
+            "/metadata/gsi/test",
+    };
+    for (const auto& dir : dirs) {
+        if (mkdir(dir.c_str(), 0700) && errno != EEXIST) {
+            std::cerr << "mkdir " << dir << ": " << strerror(errno) << "\n";
+            return false;
+        }
+    }
+
+    images_ = ImageManager::Open("/metadata/gsi/test", "/data/gsi/test");
+    if (!images_) {
+        std::cerr << "Could not open ImageManager\n";
+        return false;
+    }
+    return true;
+}
+
+bool PowerTest::Create(int argc, char** argv) {
+    if (argc < 4) {
+        usage();
+        return false;
+    }
+
+    std::string first = argv[2];
+    std::string second = argv[3];
+
+    unique_fd second_fd(open(second.c_str(), O_RDONLY));
+    if (second_fd < 0) {
+        std::cerr << "open " << second << ": " << strerror(errno) << "\n";
+        return false;
+    }
+
+    if (!Cleanup()) {
+        return false;
+    }
+    if (!SetupImages(first, second_fd)) {
+        return false;
+    }
+    if (!MapSnapshot(SnapshotStorageMode::Persistent)) {
+        return false;
+    }
+
+    struct stat s;
+    if (fstat(second_fd, &s)) {
+        std::cerr << "fstat " << second << ": " << strerror(errno) << "\n";
+        return false;
+    }
+
+    unique_fd snap_fd(open(snapshot_path_.c_str(), O_WRONLY));
+    if (snap_fd < 0) {
+        std::cerr << "open " << snapshot_path_ << ": " << strerror(errno) << "\n";
+        return false;
+    }
+
+    uint8_t chunk[4096];
+    uint64_t written = 0;
+    while (written < s.st_size) {
+        uint64_t remaining = s.st_size - written;
+        size_t bytes = (size_t)std::min((uint64_t)sizeof(chunk), remaining);
+        if (!android::base::ReadFully(second_fd, chunk, bytes)) {
+            std::cerr << "read " << second << ": " << strerror(errno) << "\n";
+            return false;
+        }
+        if (!android::base::WriteFully(snap_fd, chunk, bytes)) {
+            std::cerr << "write " << snapshot_path_ << ": " << strerror(errno) << "\n";
+            return false;
+        }
+        written += bytes;
+    }
+    if (fsync(snap_fd)) {
+        std::cerr << "fsync: " << strerror(errno) << "\n";
+        return false;
+    }
+
+    sync();
+
+    snap_fd = {};
+    if (!dm_.DeleteDeviceIfExists(kSnapshotName)) {
+        std::cerr << "could not delete dm device " << kSnapshotName << "\n";
+        return false;
+    }
+    if (!images_->UnmapImageIfExists(kSnapshotImageName)) {
+        std::cerr << "failed to unmap " << kSnapshotImageName << "\n";
+        return false;
+    }
+    if (!images_->UnmapImageIfExists(kSnapshotCowName)) {
+        std::cerr << "failed to unmap " << kSnapshotImageName << "\n";
+        return false;
+    }
+    return true;
+}
+
+bool PowerTest::Cleanup() {
+    if (!dm_.DeleteDeviceIfExists(kSnapshotName)) {
+        std::cerr << "could not delete dm device " << kSnapshotName << "\n";
+        return false;
+    }
+    if (!CleanupImage(kSnapshotImageName) || !CleanupImage(kSnapshotCowName)) {
+        return false;
+    }
+    return true;
+}
+
+bool PowerTest::CleanupImage(const std::string& name) {
+    if (!images_->UnmapImageIfExists(name)) {
+        std::cerr << "failed to unmap " << name << "\n";
+        return false;
+    }
+    if (images_->BackingImageExists(name) && !images_->DeleteBackingImage(name)) {
+        std::cerr << "failed to delete " << name << "\n";
+        return false;
+    }
+    return true;
+}
+
+bool PowerTest::SetupImages(const std::string& first, borrowed_fd second_fd) {
+    unique_fd first_fd(open(first.c_str(), O_RDONLY));
+    if (first_fd < 0) {
+        std::cerr << "open " << first << ": " << strerror(errno) << "\n";
+        return false;
+    }
+
+    struct stat s1, s2;
+    if (fstat(first_fd.get(), &s1)) {
+        std::cerr << "first stat: " << strerror(errno) << "\n";
+        return false;
+    }
+    if (fstat(second_fd.get(), &s2)) {
+        std::cerr << "second stat: " << strerror(errno) << "\n";
+        return false;
+    }
+
+    // Pick the bigger size of both images, rounding up to the nearest block.
+    uint64_t s1_size = (s1.st_size + 4095) & ~uint64_t(4095);
+    uint64_t s2_size = (s2.st_size + 4095) & ~uint64_t(4095);
+    uint64_t image_size = std::max(s1_size, s2_size) + (1024 * 1024 * 128);
+    if (!images_->CreateBackingImage(kSnapshotImageName, image_size, 0, nullptr)) {
+        std::cerr << "failed to create " << kSnapshotImageName << "\n";
+        return false;
+    }
+    // Use the same size for the cow.
+    if (!images_->CreateBackingImage(kSnapshotCowName, image_size, 0, nullptr)) {
+        std::cerr << "failed to create " << kSnapshotCowName << "\n";
+        return false;
+    }
+    if (!MapImages()) {
+        return false;
+    }
+
+    unique_fd image_fd(open(image_path_.c_str(), O_WRONLY));
+    if (image_fd < 0) {
+        std::cerr << "open: " << image_path_ << ": " << strerror(errno) << "\n";
+        return false;
+    }
+
+    uint8_t chunk[4096];
+    uint64_t written = 0;
+    while (written < s1.st_size) {
+        uint64_t remaining = s1.st_size - written;
+        size_t bytes = (size_t)std::min((uint64_t)sizeof(chunk), remaining);
+        if (!android::base::ReadFully(first_fd, chunk, bytes)) {
+            std::cerr << "read: " << strerror(errno) << "\n";
+            return false;
+        }
+        if (!android::base::WriteFully(image_fd, chunk, bytes)) {
+            std::cerr << "write: " << strerror(errno) << "\n";
+            return false;
+        }
+        written += bytes;
+    }
+    if (fsync(image_fd)) {
+        std::cerr << "fsync: " << strerror(errno) << "\n";
+        return false;
+    }
+
+    // Zero the first block of the COW.
+    unique_fd cow_fd(open(cow_path_.c_str(), O_WRONLY));
+    if (cow_fd < 0) {
+        std::cerr << "open: " << cow_path_ << ": " << strerror(errno) << "\n";
+        return false;
+    }
+
+    memset(chunk, 0, sizeof(chunk));
+    if (!android::base::WriteFully(cow_fd, chunk, sizeof(chunk))) {
+        std::cerr << "read: " << strerror(errno) << "\n";
+        return false;
+    }
+    if (fsync(cow_fd)) {
+        std::cerr << "fsync: " << strerror(errno) << "\n";
+        return false;
+    }
+    return true;
+}
+
+bool PowerTest::MapImages() {
+    if (!images_->MapImageDevice(kSnapshotImageName, 10s, &image_path_)) {
+        std::cerr << "failed to map " << kSnapshotImageName << "\n";
+        return false;
+    }
+    if (!images_->MapImageDevice(kSnapshotCowName, 10s, &cow_path_)) {
+        std::cerr << "failed to map " << kSnapshotCowName << "\n";
+        return false;
+    }
+    return true;
+}
+
+bool PowerTest::MapSnapshot(SnapshotStorageMode mode) {
+    uint64_t sectors;
+    {
+        unique_fd fd(open(image_path_.c_str(), O_RDONLY));
+        if (fd < 0) {
+            std::cerr << "open: " << image_path_ << ": " << strerror(errno) << "\n";
+            return false;
+        }
+        sectors = get_block_device_size(fd) / 512;
+    }
+
+    DmTable table;
+    table.Emplace<DmTargetSnapshot>(0, sectors, image_path_, cow_path_, mode, 8);
+    if (!dm_.CreateDevice(kSnapshotName, table, &snapshot_path_, 10s)) {
+        std::cerr << "failed to create snapshot device\n";
+        return false;
+    }
+    return true;
+}
+
+bool PowerTest::GetMergeStatus(DmTargetSnapshot::Status* status) {
+    std::vector<DeviceMapper::TargetInfo> targets;
+    if (!dm_.GetTableStatus(kSnapshotName, &targets)) {
+        std::cerr << "failed to get merge status\n";
+        return false;
+    }
+    if (targets.size() != 1) {
+        std::cerr << "merge device has wrong number of targets\n";
+        return false;
+    }
+    if (!DmTargetSnapshot::ParseStatusText(targets[0].data, status)) {
+        std::cerr << "could not parse merge target status text\n";
+        return false;
+    }
+    return true;
+}
+
+static std::string GetUserdataBlockDeviceName() {
+    Fstab fstab;
+    if (!ReadFstabFromFile("/proc/mounts", &fstab)) {
+        return {};
+    }
+
+    auto entry = android::fs_mgr::GetEntryForMountPoint(&fstab, "/data");
+    if (!entry) {
+        return {};
+    }
+
+    auto prefix = "/dev/block/"s;
+    if (!android::base::StartsWith(entry->blk_device, prefix)) {
+        return {};
+    }
+    return entry->blk_device.substr(prefix.size());
+}
+
+bool PowerTest::Merge(int argc, char** argv) {
+    // Start an f2fs GC to really stress things. :TODO: figure out data device
+    auto userdata_dev = GetUserdataBlockDeviceName();
+    if (userdata_dev.empty()) {
+        std::cerr << "could not locate userdata block device\n";
+        return false;
+    }
+
+    auto cmd =
+            android::base::StringPrintf("echo 1 > /sys/fs/f2fs/%s/gc_urgent", userdata_dev.c_str());
+    system(cmd.c_str());
+
+    if (dm_.GetState(kSnapshotName) == DmDeviceState::INVALID) {
+        if (!MapImages()) {
+            return false;
+        }
+        if (!MapSnapshot(SnapshotStorageMode::Merge)) {
+            return false;
+        }
+    }
+
+    std::random_device r;
+    std::default_random_engine re(r());
+    std::uniform_real_distribution<double> dist(0.0, 100.0);
+
+    std::optional<double> failure_rate;
+    if (argc >= 3) {
+        double d;
+        if (!android::base::ParseDouble(argv[2], &d)) {
+            std::cerr << "Could not parse failure rate as double: " << argv[2] << "\n";
+            return false;
+        }
+        failure_rate = d;
+    }
+
+    while (true) {
+        DmTargetSnapshot::Status status;
+        if (!GetMergeStatus(&status)) {
+            return false;
+        }
+        if (!status.error.empty()) {
+            std::cerr << "merge reported error: " << status.error << "\n";
+            return false;
+        }
+        if (status.sectors_allocated == status.metadata_sectors) {
+            break;
+        }
+
+        std::cerr << status.sectors_allocated << " / " << status.metadata_sectors << "\n";
+
+        if (failure_rate && *failure_rate >= dist(re)) {
+            system("echo 1 > /proc/sys/kernel/sysrq");
+            system("echo c > /proc/sysrq-trigger");
+        }
+
+        std::this_thread::sleep_for(10ms);
+    }
+
+    std::cout << "Merge completed.\n";
+    return true;
+}
+
+bool PowerTest::Check([[maybe_unused]] int argc, [[maybe_unused]] char** argv) {
+    if (argc < 3) {
+        std::cerr << "Expected argument: <new-image-path>\n";
+        return false;
+    }
+    std::string md_path, image_path;
+    std::string canonical_path = argv[2];
+
+    if (!dm_.GetDmDevicePathByName(kSnapshotName, &md_path)) {
+        std::cerr << "could not get dm-path for merge device\n";
+        return false;
+    }
+    if (!images_->GetMappedImageDevice(kSnapshotImageName, &image_path)) {
+        std::cerr << "could not get image path\n";
+        return false;
+    }
+
+    unique_fd md_fd(open(md_path.c_str(), O_RDONLY));
+    if (md_fd < 0) {
+        std::cerr << "open: " << md_path << ": " << strerror(errno) << "\n";
+        return false;
+    }
+    unique_fd image_fd(open(image_path.c_str(), O_RDONLY));
+    if (image_fd < 0) {
+        std::cerr << "open: " << image_path << ": " << strerror(errno) << "\n";
+        return false;
+    }
+    unique_fd canonical_fd(open(canonical_path.c_str(), O_RDONLY));
+    if (canonical_fd < 0) {
+        std::cerr << "open: " << canonical_path << ": " << strerror(errno) << "\n";
+        return false;
+    }
+
+    struct stat s;
+    if (fstat(canonical_fd, &s)) {
+        std::cerr << "fstat: " << canonical_path << ": " << strerror(errno) << "\n";
+        return false;
+    }
+    uint64_t canonical_size = s.st_size;
+    uint64_t md_size = get_block_device_size(md_fd);
+    uint64_t image_size = get_block_device_size(image_fd);
+    if (image_size != md_size) {
+        std::cerr << "image size does not match merge device size\n";
+        return false;
+    }
+    if (canonical_size > image_size) {
+        std::cerr << "canonical size " << canonical_size << " is greater than image size "
+                  << image_size << "\n";
+        return false;
+    }
+
+    constexpr size_t kBlockSize = 4096;
+    uint8_t canonical_buffer[kBlockSize];
+    uint8_t image_buffer[kBlockSize];
+    uint8_t md_buffer[kBlockSize];
+
+    uint64_t remaining = canonical_size;
+    uint64_t blockno = 0;
+    while (remaining) {
+        size_t bytes = (size_t)std::min((uint64_t)kBlockSize, remaining);
+        if (!android::base::ReadFully(canonical_fd, canonical_buffer, bytes)) {
+            std::cerr << "read: " << canonical_buffer << ": " << strerror(errno) << "\n";
+            return false;
+        }
+        if (!android::base::ReadFully(image_fd, image_buffer, bytes)) {
+            std::cerr << "read: " << image_buffer << ": " << strerror(errno) << "\n";
+            return false;
+        }
+        if (!android::base::ReadFully(md_fd, md_buffer, bytes)) {
+            std::cerr << "read: " << md_buffer << ": " << strerror(errno) << "\n";
+            return false;
+        }
+        if (memcmp(canonical_buffer, image_buffer, bytes)) {
+            std::cerr << "canonical and image differ at block " << blockno << "\n";
+            return false;
+        }
+        if (memcmp(canonical_buffer, md_buffer, bytes)) {
+            std::cerr << "canonical and image differ at block " << blockno << "\n";
+            return false;
+        }
+
+        remaining -= bytes;
+        blockno++;
+    }
+
+    std::cout << "Images all match.\n";
+    return true;
+}
+
+}  // namespace snapshot
+}  // namespace android
+
+int main(int argc, char** argv) {
+    android::snapshot::PowerTest test;
+
+    if (!test.Run(argc, argv)) {
+        std::cerr << "Unexpected error running test." << std::endl;
+        return 1;
+    }
+    fflush(stdout);
+    return 0;
+}
diff --git a/fs_mgr/libsnapshot/run_power_test.sh b/fs_mgr/libsnapshot/run_power_test.sh
new file mode 100755
index 0000000..dc03dc9
--- /dev/null
+++ b/fs_mgr/libsnapshot/run_power_test.sh
@@ -0,0 +1,35 @@
+#!/bin/bash
+
+set -e
+
+if [ -z "$FAIL_RATE" ]; then
+    FAIL_RATE=5.0
+fi
+if [ ! -z "$ANDROID_SERIAL" ]; then
+    DEVICE_ARGS=-s $ANDROID_SERIAL
+else
+    DEVICE_ARGS=
+fi
+
+TEST_BIN=/data/nativetest64/snapshot_power_test/snapshot_power_test
+
+while :
+do
+    adb $DEVICE_ARGS wait-for-device
+    adb $DEVICE_ARGS root
+    adb $DEVICE_ARGS shell rm $TEST_BIN
+    adb $DEVICE_ARGS sync data
+    set +e
+    output=$(adb $DEVICE_ARGS shell $TEST_BIN merge $FAIL_RATE 2>&1)
+    set -e
+    if [[ "$output" == *"Merge completed"* ]]; then
+        echo "Merge completed."
+        break
+    fi
+    if [[ "$output" == *"Unexpected error"* ]]; then
+        echo "Unexpected error."
+        exit 1
+    fi
+done
+
+adb $DEVICE_ARGS shell $TEST_BIN check $1