Image backup & disaster recovery - Backup/Restore

Computer Technology Review, August, 2003 by Morgan Edwards

With the implementation of backups with image sets, everything necessary is in place to perform a disaster recovery of a failed OS partition or disk. If a failure occurs, the following steps provide a simple and quick recovery from a network UNC path:

* Power on the equipment

* Insert the boot CD

* Boot the machine

* If unscripted, key in the UNC path to restore the machine

* Reboot the machine after the network restore is complete.

The process addressed above will automatically initiate the recovery software to restore a failed OS partition from a network UNC path.

To restore an image backup from a tape device:

* Power on the equipment (including the tape drive, if a local restore)

* Insert the desired backup tape containing an image set

* Insert the boot CD

* Boot the machine

* Select the tape device if more than one local or remote

* Select the image set to restore

* Acknowledge the partition selection (closest match is highlighted)

* Initiate the restore

* Re-boot the machine.

This process will automatically initiate the recovery software to read the tape and locate the first image set. From the list of all disks backed up by the set (there can be up to 32 disks in one image set), the operator simply selects the disk to recover and then, from a list of all available online disks, selects the target disk to initiate the physical restore.

Note that the target disk can be the original unbootable disk or a new disk right out of the box. No formatting other than a standard low-level disk format is required. Whatever was on the original disk, including multiple partitions with various operating systems, will be restored exactly as it was last backed up.

The restore process bypasses the normal operating system and therefore approaches the maximum speed that the hardware configuration is capable of sustaining (tape drive, controller, disk drive, network path, etc). After the restore process is complete, a reboot is all that is required to bring the operating system disk back to the state it was when backed up. This process also allows an administrator to go to another machine with the same or similar configuration and perform a recovery, quickly turning the alternative machine into the identity of the failed machine.

Image backup is relevant even with dynamic mirroring and clustering. Dynamic mirroring instantly mirrors corruption and file deletions. Mirroring strategic failure results in every OS partition becoming equally unbootable. A failed cluster node must also he brought back online ASAP or the Cluster Server can become a single point of failure. Few products can restore to a failed node on an active Cluster Server.

Image backup is relevant even with tile-by-file backups. While single files can be restored from image backups, the real power of image is quickly restoring a failed OS partition or disk. Since image backups can be made to UNC path, FTP and Tivoli, all machines can be protected regardless of whether tape is available or not. Image backups are basically everything in a partition or nothing. Image technology does not support file selection logic or incremental or differential backup capability. Image backups also typically bypass the file system and do not absolutely guarantee file integrity of open files. Therefore, they are a poor choice for backing up active databases like Microsoft Exchange and SQL.