Acronis Backup for Linux Server - User Guide - Manual (Page 121)

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You can choose the virtual machine type: VMware Workstation, Microsoft Virtual PC, Red Hat
Kernel-based Virtual Machine (KVM) or Red Hat Enterprise Virtualization (RHEV).
In the Storage step, you can select the virtual machine path.
What is the machine's processing power?
Conversion will take the selected machine's CPU resource. Multiple conversion tasks will be queued
on that machine and it may take considerable time to complete them all. Consider this when creating
a centralized backup plan with conversion for multiple machines or multiple local backup plans using
the same machine for conversion.
What storage will be used for the virtual machines?
Network usage
As opposed to ordinary backups (TIB files), virtual machine files are transferred uncompressed
through the network. Therefore, using a SAN or a storage local to the machine that performs
conversion is the best choice from the network usage standpoint. A local disk is not an option though,
if the conversion is performed by the same machine that is backed up. Using a NAS also makes good
sense.
Storage space
For VMware, Hyper-V and Virtual PC, disks of the resulting virtual machine will use as much storage
space as the original data occupies. Assuming that the original disk size is 100 GB and the disk stores
10 GB of data, the corresponding virtual disk will occupy about 10 GB. VMware calls this format "thin
provisioning", Microsoft uses the "dynamically expanding disk" term. Since the space is not
pre-allocated, the physical storage is expected to have sufficient free space for the virtual disks to
increase in size.
For KVM or RHEV, disks of the resulting virtual machine will have the raw format. This means that
virtual disk size is always equal to the original disk capacity. Assuming that the original disk size is 100
GB, the corresponding virtual disk will occupy 100 GB even if the disk stores 10 GB of data.
6.2.2.4 How regular conversion to VM works
The way the repeated conversions work depends on where you choose to create the virtual machine.

If you choose to save the virtual machine as a set of files: each conversion re-creates the virtual
machine from scratch.

If you choose to create the virtual machine on a virtualization server: when converting an
incremental or differential backup, the software updates the existing virtual machine instead of
re-creating it. Such conversion is normally faster. It saves network traffic and CPU resource of the
host that performs the conversion. If updating the virtual machine is not possible, the software
re-creates it from scratch.
The following is a detailed description of both cases.
If you choose to save the virtual machine as a set of files
As a result of the first conversion, a new virtual machine will be created. Every subsequent
conversion will re-create this machine from scratch. First, the old machine is temporarily renamed.
Then, a new virtual machine is created that has the previous name of the old machine. If this
operation succeeds, the old machine is deleted. If this operation fails, the new machine is deleted
and the old machine is given its previous name. This way, the conversion always ends up with a single
machine. However, extra storage space is required during conversion to store the old machine.