diff --git a/src/utils/qdl.js b/src/utils/qdl.js
index 509bd4b..a4b4001 100644
--- a/src/utils/qdl.js
+++ b/src/utils/qdl.js
@@ -4,6 +4,7 @@ import * as Comlink from 'comlink'
 
 import { getManifest } from './manifest'
 import { withProgress } from './progress'
+import { Timer } from './timer'
 
 export const Step = {
   INITIALIZING: 0,
@@ -87,6 +88,7 @@ export class QdlManager {
     this.manifest = null
     this.step = Step.INITIALIZING
     this.error = Error.NONE
+    this.timer = new Timer()
   }
 
   /**
@@ -121,6 +123,8 @@ export class QdlManager {
    * @param {number} error
    */
   setError(error) {
+    const errorName = Object.keys(Error).find((key) => Error[key] === error)?.toLowerCase()
+    this.timer.stop(`error:${errorName || error}`)
     this.error = error
     this.callbacks.onErrorChange?.(error)
     this.setProgress(-1)
@@ -135,6 +139,7 @@ export class QdlManager {
    * @param {boolean} connected
    */
   setConnected(connected) {
+    if (connected) this.timer.start()
     this.callbacks.onConnectionChange?.(connected)
   }
 
@@ -247,6 +252,7 @@ export class QdlManager {
       for await (const [image, onProgress] of withProgress(this.manifest, this.setProgress.bind(this))) {
         this.setMessage(`Downloading ${image.name}`)
         await this.imageWorker.downloadImage(image, Comlink.proxy(onProgress))
+        this.timer.mark(`download:${image.name}`)
       }
 
       console.debug('[QDL] Downloaded all images')
@@ -270,10 +276,12 @@ export class QdlManager {
 
     try {
       const currentSlot = await this.qdl.getActiveSlot()
+      this.timer.mark('get-active-slot')
       const otherSlot = currentSlot === 'a' ? 'b' : 'a'
 
       // Erase current xbl partition
       await this.qdl.erase(`xbl_${currentSlot}`)
+      this.timer.mark(`erase-xbl:${currentSlot}`)
 
       const steps = []
       const findImage = (name) => this.manifest.find((it) => it.name === name)
@@ -295,11 +303,13 @@ export class QdlManager {
         const blob = await fileHandle.getFile()
         this.setMessage(`Flashing ${partitionName}`)
         await this.qdl.flashBlob(partitionName, blob, onProgress)
+        this.timer.mark(`flash-blob:${partitionName}`)
       }
 
       console.debug('[QDL] Flashed all partitions')
       this.setMessage(`Changing slot to ${otherSlot}`)
       await this.qdl.setActiveSlot(otherSlot)
+      this.timer.mark(`set-active-slot:${otherSlot}`)
 
       this.setStep(Step.ERASING)
     } catch (err) {
@@ -320,10 +330,12 @@ export class QdlManager {
       const label = new Uint8Array(28).fill(0)  // sparse header size
       label.set(new TextEncoder().encode('COMMA_RESET'), 0)
       await this.qdl.flashBlob('userdata', new Blob([label]))
+      this.timer.mark('flash-blob:userdata')
       this.setProgress(0.9)
 
       this.setMessage('Rebooting')
       await this.qdl.reset()
+      this.timer.mark('reset')
       this.setProgress(1)
       this.setConnected(false)
 
@@ -343,9 +355,13 @@ export class QdlManager {
     await this.connect()
     if (this.error !== Error.NONE) return
     await this.downloadImages()
+    this.timer.mark('step:download-images')
     if (this.error !== Error.NONE) return
     await this.flashDevice()
+    this.timer.mark('step:flash-device')
     if (this.error !== Error.NONE) return
     await this.eraseDevice()
+    this.timer.mark('step:erase-device')
+    this.timer.stop('complete')
   }
 }
diff --git a/src/utils/timer.js b/src/utils/timer.js
new file mode 100644
index 0000000..24f3688
--- /dev/null
+++ b/src/utils/timer.js
@@ -0,0 +1,36 @@
+export class Timer {
+  /** @type {number|null} */
+  startTime = null
+
+  /** @type {Object.<string, number>} */
+  stepTimestamps = {}
+
+  start() {
+    this.startTime = performance.now()
+    this.stepTimestamps = {}
+    this.mark('start')
+  }
+
+  /**
+   * @param {string} step
+   */
+  mark(step) {
+    if (!this.startTime) return
+    const now = performance.now()
+    this.stepTimestamps[step] = now
+    console.info(`[Timer] ${step} at ${((now - this.startTime) / 1000).toFixed(2)}s`)
+  }
+
+  /**
+   * @param {string} reason
+   */
+  stop(reason) {
+    if (!this.startTime) return null
+    this.mark(reason)
+    console.debug({
+      reason,
+      totalDuration: this.stepTimestamps[reason],
+      steps: this.stepTimestamps,
+    })
+  }
+}
diff --git a/src/workers/image.worker.js b/src/workers/image.worker.js
index bfb4df1..516a6e7 100644
--- a/src/workers/image.worker.js
+++ b/src/workers/image.worker.js
@@ -52,7 +52,7 @@ const imageWorker = {
   async init() {
     if (!root) {
       root = await navigator.storage.getDirectory()
-      await root.remove({ recursive: true })
+      // await root.remove({ recursive: true })
       console.info('[ImageWorker] Initialized')
     }
 
@@ -74,6 +74,14 @@ const imageWorker = {
   async downloadImage(image, onProgress = undefined) {
     const { archiveUrl, checksum: expectedChecksum, fileName, size } = image
 
+    // Skip if already downloaded
+    try {
+      await root.getFileHandle(fileName)
+      return
+    } catch {
+      // ignored
+    }
+
     let writable
     try {
       const fileHandle = await root.getFileHandle(fileName, { create: true })