diff --git a/cli/dts/lib.deno.ns.d.ts b/cli/dts/lib.deno.ns.d.ts
index cbbf44c849..1592ee5b21 100644
--- a/cli/dts/lib.deno.ns.d.ts
+++ b/cli/dts/lib.deno.ns.d.ts
@@ -405,9 +405,9 @@ declare namespace Deno {
    *
    * ```ts
    * const source = await Deno.open("my_file.txt");
-   * const buffer = new Deno.Buffer()
    * const bytesCopied1 = await Deno.copy(source, Deno.stdout);
-   * const bytesCopied2 = await Deno.copy(source, buffer);
+   * const destination = await Deno.create("my_file_2.txt");
+   * const bytesCopied2 = await Deno.copy(source, destination);
    * ```
    *
    * @param src The source to copy from
@@ -837,7 +837,10 @@ declare namespace Deno {
    */
   export function isatty(rid: number): boolean;
 
-  /** A variable-sized buffer of bytes with `read()` and `write()` methods.
+  /**
+   * @deprecated Use Buffer from https://deno.land/std/io/buffer.ts instead. Deno.Buffer will be removed in Deno 2.0.
+   * 
+   * A variable-sized buffer of bytes with `read()` and `write()` methods.
    *
    * Deno.Buffer is almost always used with some I/O like files and sockets. It
    * allows one to buffer up a download from a socket. Buffer grows and shrinks
@@ -917,7 +920,10 @@ declare namespace Deno {
     readFromSync(r: ReaderSync): number;
   }
 
-  /** Read Reader `r` until EOF (`null`) and resolve to the content as
+  /**
+   * @deprecated Use readAll from https://deno.land/std/io/util.ts instead. Deno.readAll will be removed in Deno 2.0.
+   * 
+   * Read Reader `r` until EOF (`null`) and resolve to the content as
    * Uint8Array`.
    *
    * ```ts
@@ -938,7 +944,10 @@ declare namespace Deno {
    */
   export function readAll(r: Reader): Promise<Uint8Array>;
 
-  /** Synchronously reads Reader `r` until EOF (`null`) and returns the content
+  /**
+   * @deprecated Use readAllSync from https://deno.land/std/io/util.ts instead. Deno.readAllSync will be removed in Deno 2.0.
+   * 
+   * Synchronously reads Reader `r` until EOF (`null`) and returns the content
    * as `Uint8Array`.
    *
    * ```ts
@@ -959,7 +968,10 @@ declare namespace Deno {
    */
   export function readAllSync(r: ReaderSync): Uint8Array;
 
-  /** Write all the content of the array buffer (`arr`) to the writer (`w`).
+  /**
+   * @deprecated Use writeAll from https://deno.land/std/io/util.ts instead. Deno.readAll will be removed in Deno 2.0.
+   * 
+   * Write all the content of the array buffer (`arr`) to the writer (`w`).
    *
    * ```ts
    * // Example writing to stdout
@@ -981,7 +993,10 @@ declare namespace Deno {
    */
   export function writeAll(w: Writer, arr: Uint8Array): Promise<void>;
 
-  /** Synchronously write all the content of the array buffer (`arr`) to the
+  /**
+   * @deprecated Use writeAllSync from https://deno.land/std/io/util.ts instead. Deno.writeAllSync will be removed in Deno 2.0.
+   * 
+   * Synchronously write all the content of the array buffer (`arr`) to the
    * writer (`w`).
    *
    * ```ts
diff --git a/cli/tests/unit/fetch_test.ts b/cli/tests/unit/fetch_test.ts
index fa013f0c5b..6ece3c8351 100644
--- a/cli/tests/unit/fetch_test.ts
+++ b/cli/tests/unit/fetch_test.ts
@@ -2,12 +2,12 @@
 import {
   assert,
   assertEquals,
-  assertThrows,
   assertThrowsAsync,
   fail,
   unimplemented,
   unitTest,
 } from "./test_util.ts";
+import { Buffer } from "../../../test_util/std/io/buffer.ts";
 
 unitTest({ perms: { net: true } }, async function fetchProtocolError(): Promise<
   void
@@ -613,13 +613,13 @@ unitTest({ perms: { net: true } }, async function fetchUserAgent(): Promise<
 //     at Object.assertEquals (file:///C:/deno/js/testing/util.ts:29:11)
 //     at fetchPostBodyString (file
 
-function bufferServer(addr: string): Deno.Buffer {
+function bufferServer(addr: string): Buffer {
   const [hostname, port] = addr.split(":");
   const listener = Deno.listen({
     hostname,
     port: Number(port),
   }) as Deno.Listener;
-  const buf = new Deno.Buffer();
+  const buf = new Buffer();
   listener.accept().then(async (conn: Deno.Conn) => {
     const p1 = buf.readFrom(conn);
     const p2 = conn.write(
diff --git a/cli/tests/unit/io_test.ts b/cli/tests/unit/io_test.ts
index ba9641fdcc..c5c111e859 100644
--- a/cli/tests/unit/io_test.ts
+++ b/cli/tests/unit/io_test.ts
@@ -1,5 +1,6 @@
 // Copyright 2018-2021 the Deno authors. All rights reserved. MIT license.
 import { assertEquals, unitTest } from "./test_util.ts";
+import { Buffer } from "../../../test_util/std/io/buffer.ts";
 
 const DEFAULT_BUF_SIZE = 32 * 1024;
 
@@ -12,7 +13,7 @@ function repeat(c: string, bytes: number): Uint8Array {
   return ui8;
 }
 
-function spyRead(obj: Deno.Buffer): Spy {
+function spyRead(obj: Buffer): Spy {
   const spy: Spy = {
     calls: 0,
   };
@@ -29,8 +30,8 @@ function spyRead(obj: Deno.Buffer): Spy {
 
 unitTest(async function copyWithDefaultBufferSize() {
   const xBytes = repeat("b", DEFAULT_BUF_SIZE);
-  const reader = new Deno.Buffer(xBytes.buffer as ArrayBuffer);
-  const write = new Deno.Buffer();
+  const reader = new Buffer(xBytes.buffer as ArrayBuffer);
+  const write = new Buffer();
 
   const readSpy = spyRead(reader);
 
@@ -44,8 +45,8 @@ unitTest(async function copyWithDefaultBufferSize() {
 unitTest(async function copyWithCustomBufferSize() {
   const bufSize = 1024;
   const xBytes = repeat("b", DEFAULT_BUF_SIZE);
-  const reader = new Deno.Buffer(xBytes.buffer as ArrayBuffer);
-  const write = new Deno.Buffer();
+  const reader = new Buffer(xBytes.buffer as ArrayBuffer);
+  const write = new Buffer();
 
   const readSpy = spyRead(reader);
 
@@ -61,7 +62,7 @@ unitTest({ perms: { write: true } }, async function copyBufferToFile() {
   // bigger than max File possible buffer 16kb
   const bufSize = 32 * 1024;
   const xBytes = repeat("b", bufSize);
-  const reader = new Deno.Buffer(xBytes.buffer as ArrayBuffer);
+  const reader = new Buffer(xBytes.buffer as ArrayBuffer);
   const write = await Deno.open(filePath, { write: true, create: true });
 
   const n = await Deno.copy(reader, write, { bufSize });
diff --git a/runtime/js/12_io.js b/runtime/js/12_io.js
index fe815c7ed0..aa153e9fd6 100644
--- a/runtime/js/12_io.js
+++ b/runtime/js/12_io.js
@@ -123,6 +123,66 @@
     return result;
   }
 
+  const READ_PER_ITER = 32 * 1024;
+
+  async function readAll(r) {
+    const buffers = [];
+
+    while (true) {
+      const buf = new Uint8Array(READ_PER_ITER);
+      const read = await r.read(buf);
+      if (typeof read == "number") {
+        buffers.push(new Uint8Array(buf.buffer, 0, read));
+      } else {
+        break;
+      }
+    }
+
+    let totalLen = 0;
+    for (const buf of buffers) {
+      totalLen += buf.byteLength;
+    }
+
+    const contents = new Uint8Array(totalLen);
+
+    let n = 0;
+    for (const buf of buffers) {
+      contents.set(buf, n);
+      n += buf.byteLength;
+    }
+
+    return contents;
+  }
+
+  function readAllSync(r) {
+    const buffers = [];
+
+    while (true) {
+      const buf = new Uint8Array(READ_PER_ITER);
+      const read = r.readSync(buf);
+      if (typeof read == "number") {
+        buffers.push(new Uint8Array(buf.buffer, 0, read));
+      } else {
+        break;
+      }
+    }
+
+    let totalLen = 0;
+    for (const buf of buffers) {
+      totalLen += buf.byteLength;
+    }
+
+    const contents = new Uint8Array(totalLen);
+
+    let n = 0;
+    for (const buf of buffers) {
+      contents.set(buf, n);
+      n += buf.byteLength;
+    }
+
+    return contents;
+  }
+
   window.__bootstrap.io = {
     iterSync,
     iter,
@@ -132,5 +192,7 @@
     readSync,
     write,
     writeSync,
+    readAll,
+    readAllSync,
   };
 })(this);
diff --git a/runtime/js/40_process.js b/runtime/js/40_process.js
index cd8015e94c..a93818b95a 100644
--- a/runtime/js/40_process.js
+++ b/runtime/js/40_process.js
@@ -4,7 +4,7 @@
 ((window) => {
   const core = window.Deno.core;
   const { File } = window.__bootstrap.files;
-  const { readAll } = window.__bootstrap.buffer;
+  const { readAll } = window.__bootstrap.io;
   const { assert, pathFromURL } = window.__bootstrap.util;
 
   function opKill(pid, signo) {
diff --git a/runtime/js/40_read_file.js b/runtime/js/40_read_file.js
index 63b05b8773..0ca8f56e90 100644
--- a/runtime/js/40_read_file.js
+++ b/runtime/js/40_read_file.js
@@ -3,7 +3,7 @@
 
 ((window) => {
   const { open, openSync } = window.__bootstrap.files;
-  const { readAll, readAllSync } = window.__bootstrap.buffer;
+  const { readAll, readAllSync } = window.__bootstrap.io;
 
   function readFileSync(path) {
     const file = openSync(path);
diff --git a/runtime/js/40_write_file.js b/runtime/js/40_write_file.js
index 5964dec5f6..4662849a58 100644
--- a/runtime/js/40_write_file.js
+++ b/runtime/js/40_write_file.js
@@ -3,7 +3,6 @@
 ((window) => {
   const { stat, statSync, chmod, chmodSync } = window.__bootstrap.fs;
   const { open, openSync } = window.__bootstrap.files;
-  const { writeAll, writeAllSync } = window.__bootstrap.buffer;
   const { build } = window.__bootstrap.build;
 
   function writeFileSync(
@@ -32,7 +31,11 @@
       chmodSync(path, options.mode);
     }
 
-    writeAllSync(file, data);
+    let nwritten = 0;
+    while (nwritten < data.length) {
+      nwritten += file.writeSync(data.subarray(nwritten));
+    }
+
     file.close();
   }
 
@@ -62,7 +65,11 @@
       await chmod(path, options.mode);
     }
 
-    await writeAll(file, data);
+    let nwritten = 0;
+    while (nwritten < data.length) {
+      nwritten += await file.write(data.subarray(nwritten));
+    }
+
     file.close();
   }