While tape backups are used less frequently today for disaster recovery, they're still useful for storing data offsite in a secure location. The most effective way to back up a virtual machine (VM) is to back up the single large virtual disk file (image level) at the virtualization layer, rather than the traditional method of using an agent inside the guest operating system (file level).
Image-level backups are very useful for disaster recovery as they provide a bare-metal restore capability for virtual machines. Instead of having to restore physical servers one by one, you can restore them all to a single virtual host. While using tape for DR is slower than other alternatives, it's still a low-cost way to restore multiple virtual machines.
A disk-to-disk backup recovery is much faster than tape, and is very similar to VM replication as a virtual machine's virtual disk is mounted and then copied to another disk storage device. But, unlike replication, this approach is usually run on a scheduled basis and can be done incrementally or as a full backup. The disk target that's used can then be backed up to tape or copied to a disaster recovery site and used to quickly restore virtual machines as needed. Some apps that support this method include:
- EMC's Avamar Virtual Edition for VMware supports backups of both physical servers and virtual machines by operating at the guest OS or VM layer, and can also globally dedupe backup data. It can also do physical-to-virtual (P2V) and virtual-to-physical (V2P) recovery for maximum flexibility.
- PHD Virtual Technologies' esXpress also does both backup and replication, providing data protection and business continuity.
- Symantec Corp.'s NetBackup has very good virtualization integration and supports both disk-to-disk and disk-to-tape backups. It supports both physical and virtual servers, and can perform both image- and file-level virtual machine backups.
- Veeam Backup & Replication provides disk-to-disk backup and takes advantage of many of the new features in vSphere.
- VizionCore vRanger Pro is VizionCore's dedicated disk-to-disk backup product for virtual machines, and it supports many of the same features as their vReplicator app.
- VMware Data Recovery is included with some vSphere editions. While not as feature-rich as other products, it does provide data dedupe as well as good integration with vSphere.
Simple and built-in virtual disaster recovery methods
There are some very low-cost and simple alternatives for virtual disaster recovery, as well as some built-in tools in VMware vSphere. At the most basic level, you can use scripts to take a snapshot of a virtual machine's disk to deflect writes to it and then copy the data using FTP/SCP to another disk target such as a CIFS or NFS share. The disk target could be as basic as a removable hard disk that can be transported off-site or a device at a DR site that you copy to over a network connection. Once the virtual disk files are at the DR site, you load them on a virtual host and you'll be up and running.
VMware vCenter Converter is another tool that can be used to copy a physical server or a virtual machine to either a disk target or a virtual host; it's not very sophisticated, but it can be scripted and scheduled to make copies of servers. vSphere has some built-in high-availability (HA) and fault-tolerance technology, as well as VMware VMotion. Those features currently all require a local-area network (LAN) and aren't suitable for long-distance wide-area network (WAN) use. VMware has announced its intention to enhance the features to function over slower WAN networks.
Disaster recovery apps for Microsoft Hyper-V and Citrix Systems XenServer
Many of the same disaster recovery principles for VMware implementation also apply to Microsoft Corp.'s Hyper-V and Citrix Systems Inc.'s XenServer. There are also some applications designed specifically for Hyper-V and XenServer that can be used to implement a DR solution for those environments.
- Citrix Essentials for Hyper-V is similar to VMware Inc.'s vCenter Site Recovery Manager (SRM). It includes the StorageLink Site Recovery application that can automate DR processes and failover. It also provides integration with array-based storage replication, as well as integration with Microsoft Systems Center. A version for XenServer is expected to be released sometime in 2010.
- Marathon Technologies Corp.'s everRun suite of products provides a range of high- and continuous-availability protection for XenServer. The suite allows you to mix and match physical and virtual servers for maximum flexibility.
- Neverfail Ltd. offers a suite of continuous availability products that provide replication for Hyper-V and VMware. The products support both physical and virtual servers.
- SteelEye Technology Inc.'s SteelEye Protection Suite provides replication for Hyper-V and XenServer, as well as ESX hosts, at the VM level and is storage agnostic; it also works across a LAN or WAN.
Part of this guide was originally published in Storage magazine.