fix(backups): add random suffixes to task files to avoid collitions

See https://xcp-ng.org/forum/post/44661

@xen-orchestra/backups/writers/_MixinBackupWriter.js

@@ -43,7 +43,13 @@ exports.MixinBackupWriter = (BaseClass = Object) =>
       // merge worker only compatible with local remotes
       const { handler } = this._adapter
       if (merge && !disableMergeWorker && typeof handler._getRealPath === 'function') {
-        await handler.outputFile(join(MergeWorker.CLEAN_VM_QUEUE, formatFilenameDate(new Date())), this._backup.vm.uuid)
+        const taskFile =
+          join(MergeWorker.CLEAN_VM_QUEUE, formatFilenameDate(new Date())) +
+          '-' +
+          // add a random suffix to avoid collision in case multiple tasks are created at the same second
+          Math.random().toString(36).slice(2)
+
+        await handler.outputFile(taskFile, this._backup.vm.uuid)
         const remotePath = handler._getRealPath()
         await MergeWorker.run(remotePath)
       }

CHANGELOG.unreleased.md

@@ -15,6 +15,7 @@
 
 - [Tables/actions] Fix collapsed actions being clickable despite being disabled (PR [#6023](https://github.com/vatesfr/xen-orchestra/pull/6023))
 - [Backup] Fix `handler.rmTree` is not a function (Forum [5256](https://xcp-ng.org/forum/topic/5256/s3-backup-try-it/29) PR [#6041](https://github.com/vatesfr/xen-orchestra/pull/6041) )
+- [Backup] Fix `EEXIST` in logs when multiple merge tasks are created at the same time ([Forum #5301](https://xcp-ng.org/forum/topic/5301/warnings-errors-in-journalctl))
 
 ### Packages to release