How often should I back up my VMs, and what should the backups consist of? How do conventional and virtual backup
methods and tools differ?
Administrators must remember that virtual machine backups serve exactly the same purpose as traditional physical backups: They prevent workload damage and data loss due to human mistakes and hardware or system failures. Creating a virtual machine (VM) backup, as opposed to a snapshot, with a tool such as VMware Consolidated Backup (VCB), is designed to provide a workload with comprehensive, long-term protection.
More resources on VM backups
How to back up vSphere VMs
Avoiding common Hyper-V VM backup errors
Virtual machine backups simplified
A backup typically includes the complete contents of a VM in the form of virtual machine disk files (VMDK files) based on the Virtual Machine File System (VMFS), as well as log files, change files, paging files, configuration files and other data that completely defines the VM state. Raw device mapping (RDM) may be used in place of VMDK files when SAN-storage LUNs are connected directly to VMs.
A VM backup schedule should follow the same protocols and priorities used to back up traditional workloads. For example, a typical Windows VM may receive a complete image backup on a weekly basis, while important files may be backed up on a daily basis or even several times each day. Complete backups can require substantial time to complete. Incremental backup techniques, on the other hand, only protect data that has changed since the last backup, and allow faster and more frequent backup protection.
Backup methods and tools for virtual environments mimic conventional backup tools. For example, a backup client or agent, which is installed on the virtual server, sends backup data to a backup server. The server then writes the backup data to media such as a disk array. A scheduler automates the regular backup process by defining when to perform the process on a given VM. Backup tools are designed to run inside VMs, however, which is often a problem for non-virtualization-aware backup software.
There is the potential for workload disruption with backup tools. A VM may need to be quiesced during a backup process to prevent changes before the backup is complete. The workload is unavailable during the backup, and the disruption may be unacceptable for critical business workloads.
Tools such as VCB can reduce these disruptions by using VM snapshots as a proxy, and sending data to storage across a SAN. This eliminates the need to quiesce the VM and removes backup processing overhead so the workload's performance remains unaffected. It also eliminates the need to install a backup client on the actual production server. Instead, the client is placed on the proxy, where the snapshots are located. Essentially, VCB copies the snapshot to another server that is backed up to the SAN.
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