diff --git a/src/commands/diagnose/metrics.test.ts b/src/commands/diagnose/metrics.test.ts
new file mode 100644
index 0000000..a119911
--- /dev/null
+++ b/src/commands/diagnose/metrics.test.ts
@@ -0,0 +1,23 @@
+import { describe, it, expect } from 'vitest';
+import { formatValue } from './metrics.js';
+
+describe('formatValue', () => {
+  it('formats disk byte counters as sizes, not percentages', () => {
+    expect(formatValue('disk_total', 8511270912)).toBe('7.9 GB');
+    expect(formatValue('disk_used', 1073741824)).toBe('1.0 GB');
+    expect(formatValue('disk_database', 5242880)).toBe('5.0 MB');
+    expect(formatValue('disk_wal', 2048)).toBe('2.0 KB');
+    expect(formatValue('disk_total', 2199023255552)).toBe('2.0 TB');
+  });
+
+  it('still formats percentage metrics with a percent sign', () => {
+    expect(formatValue('disk_usage', 42.1)).toBe('42.1%');
+    expect(formatValue('cpu_usage', 7)).toBe('7.0%');
+    expect(formatValue('memory_usage', 63.25)).toBe('63.3%');
+  });
+
+  it('formats network metrics as a rate', () => {
+    expect(formatValue('network_in', 512)).toBe('512.0 B/s');
+    expect(formatValue('network_out', 1536)).toBe('1.5 KB/s');
+  });
+});
diff --git a/src/commands/diagnose/metrics.ts b/src/commands/diagnose/metrics.ts
index 6b3d91b..a39e237 100644
--- a/src/commands/diagnose/metrics.ts
+++ b/src/commands/diagnose/metrics.ts
@@ -29,23 +29,39 @@ const METRIC_LABELS: Record<string, string> = {
   cpu_usage: 'CPU Usage',
   memory_usage: 'Memory Usage',
   disk_usage: 'Disk Usage',
+  disk_used: 'Disk Used',
+  disk_total: 'Disk Total',
+  disk_database: 'Disk Database',
+  disk_wal: 'Disk WAL',
   network_in: 'Network In',
   network_out: 'Network Out',
 };
 
 const NETWORK_METRICS = new Set(['network_in', 'network_out']);
 
-function formatValue(metric: string, value: number): string {
+/** Raw byte counters — rendered as sizes, not percentages. */
+const BYTE_METRICS = new Set(['disk_used', 'disk_total', 'disk_database', 'disk_wal']);
+
+export function formatValue(metric: string, value: number): string {
   if (NETWORK_METRICS.has(metric)) {
     return formatBytes(value) + '/s';
   }
+  if (BYTE_METRICS.has(metric)) {
+    return formatBytes(value);
+  }
   return `${value.toFixed(1)}%`;
 }
 
 function formatBytes(bytes: number): string {
-  if (bytes < 1024) return `${bytes.toFixed(1)} B`;
-  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`;
-  return `${(bytes / (1024 * 1024)).toFixed(1)} MB`;
+  const KB = 1024;
+  const MB = KB * 1024;
+  const GB = MB * 1024;
+  const TB = GB * 1024;
+  if (bytes < KB) return `${bytes.toFixed(1)} B`;
+  if (bytes < MB) return `${(bytes / KB).toFixed(1)} KB`;
+  if (bytes < GB) return `${(bytes / MB).toFixed(1)} MB`;
+  if (bytes < TB) return `${(bytes / GB).toFixed(1)} GB`;
+  return `${(bytes / TB).toFixed(1)} TB`;
 }
 
 function computeStats(data: MetricDataPoint[]): { latest: number; avg: number; max: number } {