diff --git a/frontend/src/components/CursorTooltip.vue b/frontend/src/components/CursorTooltip.vue
index bd1c246..2994341 100644
--- a/frontend/src/components/CursorTooltip.vue
+++ b/frontend/src/components/CursorTooltip.vue
@@ -1,6 +1,6 @@
 <template>
   <Teleport to="body">
-    <div v-if="visible" class="cursor-tooltip" :style="tooltipStyle">
+    <div v-if="visible" ref="tooltipEl" class="cursor-tooltip" :style="tooltipStyle">
       <slot></slot>
     </div>
   </Teleport>
@@ -25,6 +25,9 @@ const props = defineProps<{
 const visible = ref(false)
 const mouseX = ref(0)
 const mouseY = ref(0)
+const tooltipWidth = ref(0)
+const tooltipHeight = ref(0)
+const tooltipEl = ref<HTMLElement | null>(null)
 let settleTimer: ReturnType<typeof setTimeout> | null = null
 let lastMoveX = 0
 let lastMoveY = 0
@@ -32,10 +35,32 @@ let lastMoveY = 0
 // Movement threshold (pixels) - cursor must settle within this radius
 const SETTLE_THRESHOLD = 8
 
-const tooltipStyle = computed(() => ({
-  left: `${mouseX.value}px`,
-  top: `${mouseY.value}px`,
-}))
+const tooltipStyle = computed(() => {
+  // Constrain to viewport
+  const pad = 8
+  let x = mouseX.value
+  let y = mouseY.value
+
+  // Only constrain if we've measured the tooltip
+  if (tooltipWidth.value > 0 && tooltipHeight.value > 0) {
+    // Adjust horizontal position if tooltip would overflow right edge
+    if (x + tooltipWidth.value + pad > window.innerWidth) {
+      x = window.innerWidth - tooltipWidth.value - pad
+    }
+    // Adjust vertical position if tooltip would overflow bottom edge
+    if (y + tooltipHeight.value + pad > window.innerHeight) {
+      y = window.innerHeight - tooltipHeight.value - pad
+    }
+    // Don't go past left/top edges
+    x = Math.max(pad, x)
+    y = Math.max(pad, y)
+  }
+
+  return {
+    left: `${x}px`,
+    top: `${y}px`,
+  }
+})
 
 // Track touch events globally to suppress touch-simulated mouse events
 const onTouchStart = () => { lastTouchTime = Date.now() }
@@ -48,6 +73,13 @@ const isTouchEvent = () => Date.now() - lastTouchTime < 500
 const showTooltip = () => {
   visible.value = true
   globalActive = true
+  // Measure tooltip after it renders
+  requestAnimationFrame(() => {
+    if (tooltipEl.value) {
+      tooltipWidth.value = tooltipEl.value.offsetWidth
+      tooltipHeight.value = tooltipEl.value.offsetHeight
+    }
+  })
 }
 
 const scheduleTooltip = () => {
@@ -131,7 +163,6 @@ defineExpose({
   backdrop-filter: blur(4px);
   -webkit-backdrop-filter: blur(4px);
   color: #fff;
-  white-space: nowrap;
   pointer-events: none;
   font-size: 1rem;
 }
diff --git a/frontend/src/components/HeaderMain.vue b/frontend/src/components/HeaderMain.vue
index 73e6ede..a52ed4c 100644
--- a/frontend/src/components/HeaderMain.vue
+++ b/frontend/src/components/HeaderMain.vue
@@ -20,6 +20,40 @@
       <span v-if="!query" class="search-hint" @click="focusSearch">/</span>
     </div>
     <div class="spacer smallgap"></div>
+    <div v-if="store.space.disk" class="disk-space"
+      @mouseenter="diskTooltip?.startHover"
+      @mousemove="diskTooltip?.updatePosition"
+      @mouseleave="diskTooltip?.endHover"
+    >
+      <svg viewBox="0 0 32 32" class="pie-mini">
+        <!-- Base: 'other' usage (light purple - appears on left, before 12 o'clock) -->
+        <circle r="16" cx="16" cy="16" fill="#c8e" />
+        <!-- Middle ring: free space (dynamic color - appears at bottom) -->
+        <circle r="8" cx="16" cy="16" fill="transparent" :stroke="freeColor" stroke-width="16" :stroke-dasharray="pieFree" :stroke-dashoffset="pieFreeOffset" transform="rotate(-90 16 16)" />
+        <!-- Top ring: storage (deep purple - appears on right after 12 o'clock) -->
+        <circle r="8" cx="16" cy="16" fill="transparent" stroke="#82d" stroke-width="16" :stroke-dasharray="pieStorage" transform="rotate(-90 16 16)" />
+        <!-- Subtle inner circle for depth -->
+        <circle r="2" cx="16" cy="16" fill="rgba(255,255,255,0.2)" />
+      </svg>
+      <CursorTooltip ref="diskTooltip" text="Disk space">
+        <div class="disk-tooltip">
+          <svg viewBox="0 0 160 80" width="160" height="80" class="pie-tooltip">
+            <!-- Pie chart centered at 40,40 -->
+            <circle r="32" cx="40" cy="40" fill="#c8e" />
+            <circle r="16" cx="40" cy="40" fill="transparent" :stroke="freeColor" stroke-width="32" :stroke-dasharray="pieFreeLg" :stroke-dashoffset="pieFreeOffsetLg" transform="rotate(-90 40 40)" />
+            <circle r="16" cx="40" cy="40" fill="transparent" stroke="#82d" stroke-width="32" :stroke-dasharray="pieStorageLg" transform="rotate(-90 40 40)" />
+            <circle r="4" cx="40" cy="40" fill="rgba(255,255,255,0.25)" />
+            <!-- Labels on the right -->
+            <rect x="78" y="10" width="10" height="10" fill="#82d" rx="2"/>
+            <text x="92" y="19" class="pie-label">{{ formatSize(store.space.storage) }} stored</text>
+            <rect x="78" y="30" width="10" height="10" fill="#c8e" rx="2"/>
+            <text x="92" y="39" class="pie-label">{{ formatSize(store.space.usage - store.space.storage) }} other</text>
+            <rect x="78" y="50" width="10" height="10" :fill="freeColor" rx="2"/>
+            <text x="92" y="59" class="pie-label">{{ formatSize(store.space.free) }} free</text>
+          </svg>
+        </div>
+      </CursorTooltip>
+    </div>
     <SvgButton name="cog" @click="settingsMenu" />
   </nav>
 </template>
@@ -27,15 +61,72 @@
 <script setup lang="ts">
 import { useMainStore } from '@/stores/main'
 import { useSsoAuthStore } from '@/stores/ssoAuth'
-import { ref, nextTick, watchEffect } from 'vue'
+import { ref, nextTick, watchEffect, computed } from 'vue'
 import ContextMenu from '@imengyu/vue3-context-menu'
 import { showAuthIframe } from 'paskia'
 import { resumeWatching } from '@/repositories/WS'
 import router from '@/router';
+import { formatSize } from '@/utils'
+import CursorTooltip from './CursorTooltip.vue'
 
 const store = useMainStore()
 const ssoStore = useSsoAuthStore()
 const search = ref<HTMLInputElement | null>()
+const diskTooltip = ref<InstanceType<typeof CursorTooltip> | null>(null)
+
+const CIRC = 50.27  // 2π×8
+
+// Storage segment (starts at top, -90°)
+const pieStorage = computed(() => {
+  const s = store.space
+  if (!s.disk) return `0 ${CIRC}`
+  const pct = s.storage / s.disk
+  return `${pct * CIRC} ${CIRC}`
+})
+
+// Free segment (starts after storage, goes clockwise to bottom area)
+const pieFree = computed(() => {
+  const s = store.space
+  if (!s.disk) return `0 ${CIRC}`
+  const pct = s.free / s.disk
+  return `${pct * CIRC} ${CIRC}`
+})
+
+const pieFreeOffset = computed(() => {
+  const s = store.space
+  if (!s.disk) return 0
+  // Start after storage segment
+  const storagePct = s.storage / s.disk
+  return -storagePct * CIRC
+})
+
+// Free space color: green when plenty, yellow when moderate, red when low
+const freeColor = computed(() => {
+  const s = store.space
+  if (!s.disk) return '#6c6'
+  const freePct = s.free / s.disk
+  if (freePct > 0.25) return '#5b5'  // Green: > 25% free
+  if (freePct > 0.10) return '#db3'  // Yellow: 10-25% free
+  return '#d44'  // Red: < 10% free
+})
+
+// Large pie for tooltip (circumference = 2π×16 ≈ 100.53)
+const CIRC_LG = 100.53
+const pieStorageLg = computed(() => {
+  const s = store.space
+  if (!s.disk) return `0 ${CIRC_LG}`
+  return `${(s.storage / s.disk) * CIRC_LG} ${CIRC_LG}`
+})
+const pieFreeLg = computed(() => {
+  const s = store.space
+  if (!s.disk) return `0 ${CIRC_LG}`
+  return `${(s.free / s.disk) * CIRC_LG} ${CIRC_LG}`
+})
+const pieFreeOffsetLg = computed(() => {
+  const s = store.space
+  if (!s.disk) return 0
+  return -(s.storage / s.disk) * CIRC_LG
+})
 
   const props = defineProps<{
   path: Array<string>
@@ -189,4 +280,23 @@ defineExpose({
   cursor: pointer;
   transition: opacity 0.15s ease;
 }
+.disk-space {
+  display: flex;
+  align-items: center;
+  cursor: default;
+}
+.pie-mini {
+  width: 1.4em;
+  height: 1.4em;
+}
+.disk-tooltip {
+  line-height: 1.5;
+}
+.pie-tooltip {
+  display: block;
+}
+.pie-tooltip .pie-label {
+  fill: #fff;
+  font-size: 9px;
+}
 </style>
diff --git a/frontend/src/repositories/WS.ts b/frontend/src/repositories/WS.ts
index c557dd3..3c8d37d 100644
--- a/frontend/src/repositories/WS.ts
+++ b/frontend/src/repositories/WS.ts
@@ -164,7 +164,8 @@ const handleWatchMessage = (event: MessageEvent) => {
       handleUpdateMessage(msg)
       break
     case !!msg.space:
-      console.log('Watch space', msg.space)
+      const store = useMainStore()
+      store.space = msg.space
       break
     case !!msg.error:
       handleError(msg)
diff --git a/frontend/src/stores/main.ts b/frontend/src/stores/main.ts
index 7b08145..9161729 100644
--- a/frontend/src/stores/main.ts
+++ b/frontend/src/stores/main.ts
@@ -80,6 +80,12 @@ export const useMainStore = defineStore('main', {
       username: '' as string,
       privileged: false as boolean,
       isLoggedIn: false as boolean,
+    },
+    space: {
+      disk: 0,
+      free: 0,
+      usage: 0,
+      storage: 0,
     }
   }),
   persist: {