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The answer to this question depends on the definition of the phrase "truly instant." I doubt instant recovery of virtual machines can be made to occur within a matter of milliseconds, at least not in the near future. However, it may be possible to speed up instant VM recovery to the point that it occurs in a matter of seconds.
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To see why this is the case, you need to consider the way instant VM recovery works. Each vendor has its own way of implementing instant VM recovery, but, as a general rule, instant recovery features are based around the use of differencing disks.
Instant recovery requires the following elements:
- There must be human interaction. The administrator must recognize the need for a recovery operation and initiate the process. Instant VM recovery is different from high availability in that recovery does not happen automatically.
- The backup server must create some differencing disks. The backup copy of a VM will be used to run production workloads, so the virtual hard disk that exists within the backup must remain in pristine condition to preserve the integrity of the backup.
- One of the differencing disks must intercept write operations from the VM itself. When the backup copy of the VM is mounted and started, any write operations will be redirected to the differencing disk in an effort to prevent the backup from being overwritten. Some backup solutions create a second differencing disk that can be used to intercept future backup operations, so the original backup is not modified.
If the goal is to make instant VM recovery truly instant, these two situations need to change:
- The human element must be removed. The system must be smart enough to recognize the need for recovery on its own.
- The amount of time required to create virtual hard disks and mount the VM must be reduced. It is possible this could be achieved through the use of RAM caching and high-speed flash media.
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