diff --git a/bench/files.ts b/bench/files.ts
new file mode 100644
index 0000000..b60d8d1
--- /dev/null
+++ b/bench/files.ts
@@ -0,0 +1,53 @@
+import { bench, do_not_optimize, group, run } from 'mitata';
+import { mkdtemp, rm } from 'node:fs/promises';
+import { tmpdir } from 'node:os';
+import { join } from 'node:path';
+import { createFileSystem } from '../mod.ts';
+import { createMemoryAdapter } from '../src/adapter/memory.ts';
+import { createNodeAdapter } from '../src/adapter/node.ts';
+
+const chunk = new Uint8Array(64 * 1024);
+
+/** Writes one native file through a single long-lived positional resource. */
+async function native(bytes: number): Promise<number> {
+  const root = await mkdtemp(join(tmpdir(), 'opfs-bench-'));
+  const fileSystem = createFileSystem(createNodeAdapter({ root }), { coordination: 'local' });
+  try {
+    await fileSystem.ensureFile('/output.bin');
+    const file = await fileSystem.openWritableFile('/output.bin');
+    try {
+      for (let at = 0; at < bytes; at += chunk.byteLength) await file.write(chunk, { at });
+      await file.flush();
+      await file.close();
+    } catch (error) {
+      await file.abort(error);
+      throw error;
+    }
+    const stat = await fileSystem.stat('/output.bin');
+    return stat.kind === 'file' ? stat.size : 0;
+  } finally {
+    await fileSystem.close();
+    await rm(root, { recursive: true, force: true });
+  }
+}
+
+/** Exercises the intentionally expensive record-update path as a pathological comparison. */
+async function record(bytes: number): Promise<number> {
+  const fileSystem = createFileSystem(createMemoryAdapter(), { coordination: 'local' });
+  try {
+    for (let at = 0; at < bytes; at += chunk.byteLength) {
+      await fileSystem.writeFile('/output.bin', chunk, { mode: 'update', at, parents: true });
+    }
+    const stat = await fileSystem.stat('/output.bin');
+    return stat.kind === 'file' ? stat.size : 0;
+  } finally {
+    await fileSystem.close();
+  }
+}
+
+group('@okikio/opfs positional output', () => {
+  bench('Node positional 16 MiB', async () => do_not_optimize(await native(16 * 1024 * 1024))).gc('once');
+  bench('record update 1 MiB pathological', async () => do_not_optimize(await record(1024 * 1024))).gc('once');
+});
+
+await run();