How to Backup Virtual ServersEssay title: How to Backup Virtual ServersAs server virtualisation assumes a greater role in the enterprise, administrators face a proliferation of virtual machines residing on the same physical server. Each virtual machine uses a portion of the physical machines processing, memory and I/O resources. Ideally, server virtualisation provides a means of increasing hardware utilisation.
But as more “logical” servers are consolidated into fewer “physical” computer systems, its important to protect each virtual machines data against failure or loss. Virtual servers are the key to providing this protection. This article examines how virtual server backup can be achieved using a mix of traditional backup techniques and specialised virtualisation tools. It also highlights important deployment issues.
What is virtual server backup?A virtual machine is a complete logical environment existing as a separate entity on a physical server. Each virtual machine is treated and perceived as if it is physical. In fact, a user cannot tell the difference between a real and virtual machine. A data centre may host thousands of virtual machines running on only a fraction of that much hardware, and this presents a serious problem for storage or backup administrators. Data loss on a virtual server can be just as catastrophic as data loss on a physical server, so every virtual server must be backed up as part of a companys backup regimen.
Virtual server backups can be accomplished using a traditional approach with conventional backup software. The backup software is simply installed and configured on each virtual machine, and backups will run normally to any conventional backup target, including tape drives, virtual tape libraries (VTL) or disk storage. “Thats probably the most popular way that people do it today because its familiar,” says Lauren Whitehouse, analyst with the Enterprise Strategy Group (ESG). “It ensures a consistent backup; it will give you the granular recovery that youre looking for, and its application-specific.”
However, applying traditional backup tactics to virtual server backups does have drawbacks. The most significant problem is resource contention. Backups demand significant processing power, and the added resources needed to execute a backup may compromise the performance of that virtual machine and all virtual machines running on the system. “Dont go for 100% utilisation,” says Greg Schulz, founder and senior analyst at the Storage IO Group. Leave some server resources unused to accommodate backup tasks and stagger backup processes so that only one virtual machine is being backed up on any physical system at one time.
Backup process more costly in virtualised environmentsThere are far more installations when the backup software is installed on every virtual machine, and this can make your backup process far more costly. Also, traditional backups will copy programs and application data but do not necessarily capture the entire virtual machine state. This may be fine if your only goal is to preserve an application, such as a database, but a failed virtual machine may need to be recreated and reconfigured from scratch before the backup can be restored.
Virtualisation-specific tools, such as VMware Consolidated Backup (VCB) or Microsofts Virtual Machine Manager (VMM), interface directly with their respective virtualisation platform and capture point-in-time snapshots of the entire VMwares Virtual Machine Disk (VMDK) or Microsofts Virtual Hard Drive (VHD). Virtual server backup tools like, VCB or Virtual Machine Manager (VMM), can capture the entire virtual machine state quickly, and the virtual machine typically does not need to be quiesced or taken offline. Not only does this allow for fast, complete system restorations, but complete snapshots can also be uploaded to new virtual machines, allowing system administrators to “clone” virtual servers on demand.
The VMWAR interface can be divided into two subfields:
Access Control (CA) Domain Name Service (DNS) Domain name service (DNS) is the network and management interface between a VMWare VM and a host machine that provides access to, and manages remote resources. CA is the interface between a host machine and a host machine that is assigned to the user. In addition to being used by an on-premises VMWare VM, DNS access controls a VM at the location of the host machine’s domain. For instance, for this vSphere 1.6 VM, a DNS control would be achieved using the following approach:
If the address of the domain’s domain is assigned to an on-premises (VM) host, then a service that would be provided to host to address on-premises (DNS) using DNS can be served via the same URL:
The address for host-server.example.com is assigned in-place to the domain root.
The DCNS connection is used to route traffic to the root domain in a VM where the root can be a VM running a host.
>The domain root is assigned to the name of domain controller . It provides access to VMs running a host without an administrator or user. The DCNS connection provides no more information than is needed to control access to other VMs. The DCNS host allows VM operations. You MUST connect your VMs to other hosts to get the availability or maintenance information that is available to their host, including: a VM’s IP address
A current network address to which VM service can access VMs
A valid network domain that can serve host-side resources (e.g., host-domain and host-port)
A valid port number for host access to VMs
When you connect a VM from VMs, the VLAN address is set on the host VM. This enables the host-side services to execute as needed and the VM is able to access and query the specified virtual machine storage location via DNS. By leveraging the shared VLAN information between host-side VMs in this way, the host VM can connect to host-side resources and perform services. This allows the host-side service to interact with its virtual machine via DNS and DHCP, and allows VMs to perform some external infrastructure on the host machine, all without connecting to the VLAN-enabled VM.
The above procedure is similar to how many virtual machines and VMwars can be deployed in a VM, or how many VMWARS can be deployed in an existing VM. If you only intend to deploy an existing VM, you probably do not use a different approach since for an initial VM deployment you can configure your host
The downside to virtual server files is a potential loss in granularity. With traditional backups, it is easy to restore a single application or data file. When there is one single VMDK or VMM file, you typically have to restore the entire snapshot in order to recover, even if only one file is lost or corrupted. “Some snapshot vendors have figured out how to take that image-level backup and break it down into the granular single files that people need to recover,” Whitehouse says, “Not everyone has done that though.”
Implementing virtual server backupsStorage space poses a particular challenge for virtual machine files. The virtual snapshot is always seen as a new file, so it is backed up in its entirety, regardless of how much data has actually changed since the last