# Features

## Application-aware backup

In **Xopero ONE**, you can enable **application-aware** backups for **Windows Server** virtual machines, which allows you to create consistent backups. This functionality is based on **Microsoft VSS** (**Volume Shadow Copy Service**), which silences applications and suspends write requests for **up to 60 seconds**. **VSS** flushes the file system buffer and freezes the file system, ensuring that metadata is saved and data is written in a consistent order. You can also enable the **Continue backup on errors** option, which allows the backup to proceed even if **application-aware** issues occur.

***

## Hyper-V RCT

### <mark style="background-color:$primary;">Definition</mark>

**Hyper-V RCT** (**Resilient Change Tracking**) is a built-in feature of the **Hyper-V** architecture that tracks changes in the disk blocks of virtual machines. Similar to **VMware**’s **Changed Block Tracking** (**CBT**), it greatly improves the efficiency of data backup operations. **RCT** allows incremental and differential backups to run faster and more effectively by providing a direct list of changed blocks since the last backup, eliminating the need to compare current VM disk data with previous backup versions.

### <mark style="background-color:$primary;">How it works</mark>

**RCT** works by maintaining a dedicated change tracking log for every virtual disk connected to a VM. This log keeps track of all disk blocks that have been modified since the last backup. When a backup starts, **RCT** supplies the backup software with a list of these changed blocks, allowing it to copy only the modified data. The tracking log is continuously updated after each backup, ensuring that future backup operations remain fast, incremental, and efficient.

### <mark style="background-color:$primary;">Use cases</mark>

1. **Incremental backups** — **RCT** is highly effective for incremental backups, as it identifies and captures only the data blocks that have changed since the last backup. This approach greatly reduces both the backup duration and storage consumption.
2. **Differential backups** — in case of differential backups, which include all changes made since the last full backup, **RCT** simplifies the process by directly identifying the modified blocks. This makes differential backups faster, more reliable, and easier to manage.

***

## Skip disks

### <mark style="background-color:$primary;">Definition</mark>

The **skip disks** feature in **Hyper-V** allows the backup process to omit certain disks from snapshot creation. This applies to disks where snapshots are not supported or practical, such as shared disks or physical disks directly attached to a virtual machine. By skipping these disks, **Hyper-V** ensures that the backup operation can continue smoothly without errors or interruptions, maintaining the overall stability and reliability of the backup process.

**Skip disks** feature highlights **Xopero ONE**’s adaptability and commitment to delivering a seamless backup experience, even in complex virtualized environments. By leveraging this feature, IT administrators can optimize backup performance, increase flexibility, and ensure reliable protection of their virtual infrastructure against data loss and downtime.

### <mark style="background-color:$primary;">Use cases</mark>

1. **Shared Virtual Hard Disks (VHDX)** — when virtual machines use shared **VHDX** files for clustering, these disks typically cannot be snapshotted. The **skip disks** feature allows such configurations to be backed up while excluding the shared **VHDX**, ensuring the process completes successfully.
2. **Physical disks** — for VMs that use physical disks through pass-through functionality (directly attached storage), standard snapshot methods do not apply. By skipping these disks, the backup can proceed smoothly, protecting the rest of the environment without interruption.
3. **Virtual machines with Fibre Channel adapters** — VMs configured with **Fibre Channel** adapters may encounter backup failures if the **skip disks** option is not enabled. Using this feature prevents such errors and helps maintain the stability and reliability of the backup operation.