Virtual server backup using traditional techniques and specialised tools

But as more "logical" servers are consolidated into fewer "physical" computer systems, it's important to protect each virtual machine's data against failure or loss. Virtual server backups 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 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 company's backup regime.

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 (VTLs) or disk storage.

"That's probably the most popular way that people do it today, because it's familiar," says Lauren Whitehouse, analyst with research firm Enterprise Strategy Group (ESG). "It ensures a consistent backup, it will give you the granular recovery that you're looking for, and it's application-specific."

However, applying traditional backup tactics to virtual server backups does have drawbacks. The biggest 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.

The biggest problem in applying traditional backup tactics to virtual server backups is resource contention.

"Don't go for 100% utilisation," says Greg Schulz, founder and senior analyst at storage research firm Storage IO Group. Instead, he suggests that users leave some server resources unused to accommodate backup tasks. He also recommends staggering 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 environments

There are far more installations where the backup software is installed on every virtual machine, even though 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 Microsoft's Virtual Machine Manager (VMM) interface directly with their respective virtualisation platform and capture point-in-time snapshots of the entire VMware Virtual Machine Disk (VMDK) or Microsoft Virtual Hard Drive (VHD).

Virtual server backup tools like VCB or 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 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 backups

Storage 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 snapshot. Snapshots will continue to use the full backup window and consume the same amount of disk/tape space.

Data deduplication, also called single-instance storage, can help reduce these storage demands. Deduplicating at the storage system doesn't shrink the backup window because data still must be transferred across the network prior to deduplication. Experts suggest deduplicating through an appliance or at the source to save backup media while minimising the backup window.

Virtual server backups have no specific affinity for backup targets. Traditional backups can go to tape, VTL or other disk systems as they do now, though most performance-minded users will back up to some form of disk storage first, then offload the backup to tape later. VCB or VMM backups are almost universally sent to disk, then later replicated to offsite disk storage or sent to tape. Backup media is then retained or stored exactly the same way as conventional backups. However, retention periods should be evaluated carefully; it may not be necessary to save every snapshot for a prolonged period. Consult your local retention experts or legal counsel for their recommendations.

Virtual server backups should also be verified and tested periodically to ensure that the required suite of data has been adequately captured, but this typically involves restoring the backup to another virtual server and verifying normal operation. For shops that perform frequent restorations, the "testing" process may be ongoing; backups are tested each time a file or application needs to be restored. Other virtualised shops have auxiliary machines available for testing purposes, which allows administrators to periodically test backups without taking the original production machines offline.

Companies performing virtual server backups

For Young America Corp., the customer fulfillment business generates a great deal of customer data. Close to 20 TB of production data and 10 TB of development and test data is spread across several EMC platforms running under VMware's Infrastructure 3 virtualisation software.

Virtualisation has proven its value to the organisation. "The No. 1 [benefit] is efficient use of resources," says Dan Thompson, network engineer at Young America. "Secondary [benefits] include ease of backups and disaster recovery."

Thompson backs up virtual machines using VCB operated in concert with EMC's Legato backup software. Virtual server backups are performed nightly along with the entire backup process and are also performed on-demand. The entire backup process takes six to seven hours each night. But with about 160 servers to contend with -- half of them virtual servers -- it's difficult to say exactly how long a single virtual machine backup takes.

The No. 1 benefit of virtualisation is efficient use of resources. Dan Thompson network engineer, Young America Corp.

In addition to protecting existing virtual servers, Thompson also uses virtual snapshots to clone new servers. "You can use VCB to actually save a copy of a virtual machine 'hot,' then you can restore it to another virtual machine and bring it up as a clone of the first one," he says.

An EMC Clariion Disk Library provides virtual tape support. "The backup application backs up to that and also to actual [IBM] tape, so we go to both," Thompson says, noting that the current LTO-3 tape drives will soon be upgraded to LTO-4. Although Thompson has never needed to restore a virtual machine failure, the restoration process has been thoroughly proven and is tested at least monthly.

There were some early difficulties. At first the virtual machines locked up when VCB was executed, which was attributed to outdated VMware drivers and tools. But once that was resolved, he says, the virtual machines haven't had a problem. This underscores the importance of software maintenance and version control in a virtual server environment.

After efficiency, flexibility in integrating infrastructures is probably the most important benefit gained from server virtualisation. For information services business Kroll Factual Data, the flexibility afforded by Microsoft Virtual Server 2005 R2 proved critical when it needed to move the technology infrastructure of a company it had acquired into its data centre. "The virtual environment was really the only way that we could be flexible enough to tackle the integration in a timely manner," says Christopher M. Steffen, manager of information security and compliance.

Once the benefits of storage virtualisation became clear, the entire infrastructure was migrated to a virtual server environment, supporting more than 600 virtual machines in production (80-85% of the production environment). There are another 400 virtual machines in disaster recovery and 400 more in development.

"It's a hardware-agnostic point of view," Steffen says. "Any platform that runs a Windows server can support full virtualisation and really utilise your hardware to its fullest potential." Today, Kroll Factual Data operates about 60 TB of storage on an IBM FAStT storage server.

Steffen uses the VMM utility to manage and back up Microsoft virtual machines. Not only does VMM help configure and optimise the virtual environment, it also creates backup snapshots of the VHD file. Steffen also uses VMM to create standard server "images" that speed the deployment of new virtual servers, while helping to prove the compliance of software/driver versions across the environment. "Instead of configuring a new server from scratch, which can take two to four hours, just take and copy the hardened image that you've already created and patched correctly up to the host machine," he says. "That takes 10 to 15 minutes."

Almost all virtual machine backups are performed through VMM, though there are still some manual backup processes to accommodate mission-critical processes that have not yet been virtualised. The actual time needed to back up a virtual server depends on the size of the VHD file and the bandwidth available to pass the backup data to the target. Backups are always sent to disk first, then offloaded to tape as a separate process.

The ability to configure disaster recovery sites virtually anywhere, where power and Internet access are available, was an important benefit, according to Steffen. "Virtualisation makes the whole disaster recovery 'mess' actually something that is manageable," he says. "And VMM helps with configuration management and [to] update migration." VMM provides load-balancing recommendations that can help to optimise the number of virtual machines on each server.

Future of virtual server backups

Continually growing storage volumes will inevitably lead to a demand for more network storage for virtual machine backups. This will also usher in greater application awareness and data deduplication with virtual server backups. At this point, the real challenge will be to implement deduplication without compromising virtual machine performance.

"If you run dedupe on a virtual machine, you'll put more workload on the virtual machine [CPU]," Schulz says. In the near term, an external data deduplication appliance may be required to achieve performance goals. Other performance issues related to server virtualisation will be increasingly addressed using optimised hardware chipsets, such as Intel's vPro Processor Technology and Q35 Express Chipset.

While conventional backups will rely upon backup software for proper restoration, affording a small amount of native security, virtual machines are complete self-standing system snapshots that are far simpler to restore than a backup volume. Encryption is another component in the virtual backup environment, but few virtualisation users have as yet made security a top priority.

Ultimately, the future of such tools remains murky. Virtualisation vendors may shift the backup burden to third-party developers. "The first step for [virtualisation vendors] would be to create APIs for backup vendors," Whitehouse says. Backup vendors could then build new applications, she notes, or add features to their existing backup products that would utilise those APIs to provide more refined backup products.

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