Symptoms

1) An Entire machine backup fails with the following error:

ASYNC: Full barrier action job

Example of error log

Error code: 4
Module: 249
Line info: 0xd7761d47edeb39a4
Fields: {"$func":"Async::Detail::SemaphoreLogic::SemaphoreJob::Describe","$module":"ms_vsa64_27009","$line":"154","$file":"d:\\1759\\enterprise\\common\\async\\semaphore.cpp"}
Message: ASYNC: Action sequence pending action job.
------------------------
Error code: 4
Module: 249
Line info: 0x368cb7423c1c08db
Fields: {"$func":"Async::FullBarrier::BarrierJob::Describe","$module":"ms_vsa64_27009","$line":"227","$file":"d:\\1759\\enterprise\\common\\async\\full_barrier.cpp"}
Message: ASYNC: Full barrier action job.

2) SnapAPI logs contain entries about disks with zero signature:

[20211006-210003-549][SnapAPI][T] Disk 00000057322CA650: Read MBR
[20211006-210003-549][SnapAPI][T] NTSignature: 0x0

Cause

In most cases, this issue appears when a special USB stick (such as Technical Security Module or similar tool for encryption and/or access protection) with protected MBR is connected to the machine.

When preparing for a disk backup, Acronis Cyber Protect reads the NT signatures of disks. The protected USB stick has a zero NT signature, and the program attempts to generate a random NT signature and assign it to this disk, so it can be identified, but the operation fails because MBR on this media is write-protected.

Solution

There are two possible workarounds:

1. If possible, remove MBR protection from the protected USB stick(or disk) using the manufacturer's tools, and run a backup. After the first backup is successfully created, you can reenable the protection, backups by the same backup plan should work correctly after that.
2. Instead of an Entire machine backup, configure a disk/partition backup and select the necessary disks directly. Unplug the protected USB stick while configuring the backup.