PROBLEM
- When restoring a disk image using Shadowprotect console or Recovery Environment (boot CD), restore throughput is much slower than file copy speeds from the same disk or network share. For example, if a file copies at 100MB/s, a restore from the same location may only run at 10MB/s.
CAUSE
- Restore operations are not comparable to file copy. The restore process accesses data contained within the chain of backup images and then restores the specific data from where it resides on the original source disk to the exact same location on the disk of the target volume.
- The longer the incremental "chain", the longer the process can take. A single incremental image will only contain a certain percentage of the data. The restore process must go back through all the image files (incrementals, and consolidated files) to get a full picture of data that needs to be changed.
- Typically, restore is faster from a local disk than a network share. This removes the network layer from the equation and allows faster I/O for the restore process when accessing the image files.
RESOLUTION
For reasons given above, it is normal that restore speeds are significantly slower than file copy speeds. The following steps may help to improve performance in some cases:-
- avoid long chains of incremental backups. If using "continuous incremental" schedule, ensure that ImageManager is used for regular consolidation.
- ensure network and/or disk system drivers are up-to-date. When using Recovery Environment, WinPE will utilize default drivers that it can find that matches the hardware of the machine running the restore operation. You may see increased throughput by adding specific drivers for the WinPE environment and the networking hardware on the system being used.
- if backup images are on a network share, copying them to locally attached drive prior to restore may improve performance.
PREVENTING RECURRENCE
- To improve future recovery times, consider using the Headstart Restore (HSR) feature in ImageManager. HSR is used to run the restore process pro-actively as images are created, and will cut down on the recovery time in the event of a system outage.