diff --git a/@xen-orchestra/backups/_cleanVm.integ.spec.js b/@xen-orchestra/backups/_cleanVm.integ.spec.js
index 5ed5d2b8f15..0d3a1b1989a 100644
--- a/@xen-orchestra/backups/_cleanVm.integ.spec.js
+++ b/@xen-orchestra/backups/_cleanVm.integ.spec.js
@@ -9,6 +9,7 @@ const crypto = require('crypto')
 const { RemoteAdapter } = require('./RemoteAdapter')
 const { VHDFOOTER, VHDHEADER } = require('./tests.fixtures.js')
 const { VhdFile, Constants, VhdDirectory, VhdAbstract } = require('vhd-lib')
+const { checkAliases } = require('./_cleanVm')
 const { dirname, basename } = require('path')
 
 let tempDir, adapter, handler, jobId, vdiId, basePath
@@ -406,3 +407,23 @@ describe('tests multiple combination ', () => {
     }
   }
 })
+
+test('check Aliases should work alone', async () => {
+  await handler.mkdir('vhds')
+  await handler.mkdir('vhds/data')
+  await generateVhd(`vhds/data/ok.vhd`)
+  await VhdAbstract.createAlias(handler, 'vhds/ok.alias.vhd', 'vhds/data/ok.vhd')
+
+  await VhdAbstract.createAlias(handler, 'vhds/missingData.alias.vhd', 'vhds/data/nonexistent.vhd')
+
+  await generateVhd(`vhds/data/missingalias.vhd`)
+
+  await checkAliases(['vhds/missingData.alias.vhd', 'vhds/ok.alias.vhd'], 'vhds/data', { remove: true, handler })
+
+  // only ok have suvived
+  const alias = (await handler.list('vhds')).filter(f => f.endsWith('.vhd'))
+  expect(alias.length).toEqual(1)
+
+  const data = await handler.list('vhds/data')
+  expect(data.length).toEqual(1)
+})
diff --git a/@xen-orchestra/backups/_cleanVm.js b/@xen-orchestra/backups/_cleanVm.js
index a58973dda4f..f2f551f4d03 100644
--- a/@xen-orchestra/backups/_cleanVm.js
+++ b/@xen-orchestra/backups/_cleanVm.js
@@ -1,7 +1,7 @@
 const assert = require('assert')
 const sum = require('lodash/sum')
 const { asyncMap } = require('@xen-orchestra/async-map')
-const { Constants, mergeVhd, openVhd, VhdAbstract, VhdFile } = require('vhd-lib')
+const { Constants, isVhdAlias, mergeVhd, openVhd, VhdAbstract, VhdFile, resolveAlias } = require('vhd-lib')
 const { dirname, resolve } = require('path')
 const { DISK_TYPES } = Constants
 const { isMetadataFile, isVhdFile, isXvaFile, isXvaSumFile } = require('./_backupType.js')
@@ -82,6 +82,7 @@ async function mergeVhdChain(chain, { handler, onLog, remove, merge }) {
     )
 
     clearInterval(handle)
+    onLog(`merging ${child} into ${parent} done`)
 
     await Promise.all([
       VhdAbstract.rename(handler, parent, child),
@@ -103,6 +104,7 @@ const noop = Function.prototype
 const INTERRUPTED_VHDS_REG = /^(?:(.+)\/)?\.(.+)\.merge.json$/
 const listVhds = async (handler, vmDir) => {
   const vhds = []
+  const aliases = {}
   const interruptedVhds = new Set()
 
   await asyncMap(
@@ -120,7 +122,7 @@ const listVhds = async (handler, vmDir) => {
             filter: file => isVhdFile(file) || INTERRUPTED_VHDS_REG.test(file),
             prependDir: true,
           })
-
+          aliases[vdiDir] = list.filter(vhd => isVhdAlias(vhd))
           list.forEach(file => {
             const res = INTERRUPTED_VHDS_REG.exec(file)
             if (res === null) {
@@ -134,8 +136,54 @@ const listVhds = async (handler, vmDir) => {
       )
   )
 
-  return { vhds, interruptedVhds }
+  return { vhds, interruptedVhds, aliases }
+}
+
+async function checkAliases(aliasPaths, targetDataRepository, { handler, onLog = noop, remove = false }) {
+  const aliasFound = []
+  for (const path of aliasPaths) {
+    const target = await resolveAlias(handler, path)
+
+    if (!isVhdFile(target)) {
+      onLog(`Alias ${path} references a non vhd target:  ${target}`)
+      if (remove) {
+        await handler.unlink(target)
+        await handler.unlink(path)
+      }
+      continue
+    }
+
+    try {
+      const { dispose } = await openVhd(handler, target)
+      dispose()
+    } catch (e) {
+      onLog(`target ${target} of alias ${path} is missing or broken`)
+      if (remove) {
+        try {
+          await VhdAbstract.unlink(handler, path)
+        } catch(e){}
+      }
+      continue
+    }
+
+    aliasFound.push(resolve('/', target))
+  }
+
+  const entries = await handler.list(targetDataRepository, {
+    ignoreMissing: true,
+    prependDir: true,
+  })
+
+  entries.forEach(async entry => {
+    if (!aliasFound.includes(entry)) {
+      onLog(`the Vhd  ${entry} is not referenced by a an alias`)
+      if (remove) {
+        await VhdAbstract.unlink(handler, entry)
+      }
+    }
+  })
 }
+exports.checkAliases = checkAliases
 
 const defaultMergeLimiter = limitConcurrency(1)
 
@@ -180,8 +228,12 @@ exports.cleanVm = async function cleanVm(
       }
     }
   })
-
-  // @todo : add check for data folder of alias not referenced in a valid alias
+  // check if alias are correct
+  // check if all vhd in data subfolder have a corresponding alias
+  await asyncMap(Object.keys(vhdsList.aliases), async dir => {
+    const aliases = vhdsList.aliases[dir]
+    await checkAliases(aliases, `${dir}/data`, { handler, onLog, remove })
+  })
 
   // remove VHDs with missing ancestors
   {
diff --git a/CHANGELOG.unreleased.md b/CHANGELOG.unreleased.md
index 524e6ec0c6d..aa748f7484b 100644
--- a/CHANGELOG.unreleased.md
+++ b/CHANGELOG.unreleased.md
@@ -7,6 +7,8 @@
 
 > Users must be able to say: “Nice enhancement, I'm eager to test it”
 
+- [Backup] Add sanity check of alias after backup. PR [6043](https://github.com/vatesfr/xen-orchestra/pull/6043)
+
 ### Bug fixes
 
 > Users must be able to say: “I had this issue, happy to know it's fixed”