One recurring question we get is, “How do I test the integrity of my ShadowProtect backup images?” Tragically, this question sometimes comes while a partner is trying to recover his data. During all the years I was the technician responsible for disaster recovery (DR) planning at StorageCraft, testing was always an aspect that was very challenging.
The old days of backup and DR testing
In those days, I had two tests I could perform myself:
- Restore backup from tape to disk, or
- Schedule a DR test with SunGard in Atlanta.
Option One required me to mount about 100 x 12-inch tapes and restore them to disk. That operation of restoring 16GB total disk storage took a week. It also required a lot of disk-jockeying because enterprise-quality disk drives were extremely expensive.
Option Two was very expensive. You needed to ship those tapes several weeks in advance to pre-stage the test. After that, we had to take someone from each department to Atlanta to perform the verification of the recovery.
Even then, we couldn’t attach to real-time feeds or connect to the plant floor systems (the test was more or less a financial and process test). We could never set up the necessary communications and remote equipment.
SPX and ShadowProtect backup testing today
Fast forward to today, and the world is a much kinder place for our partners and customers conducting DR testing—in large part because of StorageCraft VirtualBoot technology.
Here are some of the backup image verification methods that you can use and a little info on the types of verifications they provide.
ImageManager Image Verification
ImageManager immediately performs a checksum verification on any backup images in a folder it’s monitoring. (StorageCraft ImageManager is our free image management tool.)
Pros: Verifies the integrity of the images in a chain against corruption. Corruption may occur with disk degradation (like bad blocks) and viruses that might have attacked the backup images after the image was created. Essentially it confirms that the SPX or ShadowProtect checksum calculation has not changed since the image was created.
Cons: If a virus or a logical block is already corrupt on the system being backed up, that corruption would not be exposed by the ImageManager automated checksum verification. As the dinosaurs of my day used to say, “Garbage in. Garbage out.”
Using the Mount option (found within the SPX or ShadowProtect interface) provides a basic check of the image chain integrity. If ImageManager completes verification, Mount can be used to test another aspect of the chain integrity.
Pros: The Mount operation can be used to do a check of the chain. You can also use it to access files for quick recovery and, in write mode, to remove viruses that might have gone undetected on the system being backed up.
Cons: It may not confirm that the system can be recovered, since any corruptions might only expose themselves in a live operating system with live, functioning applications.
VirtualBoot provides a boot verification of the backup image chain and allows the actual confirmation of applications inside the backup.
Pros: Confirms that the image chain is bootable. The user can then log in and test application functionality. Now that ImageManager features Advanced Verification, the boot process is automated, and you’ll receive a screenshot of the running virtual machine’s login screen, thereby confirming that the images are bootable.
Cons: It may not prove completely that there are no boot issues with the chain because a virus could have been backed up or bad blocks could have been copied before they were replaced by the original system. If the virus is dormant or bad blocks were copied but are not referenced at boot time, then there is a possibility that some corruption may exist.
VirtualBoot is the most thorough and most automated way to confirm SPX and ShadowProtect backups are bootable. But it does not find all of the various types of possible image data corruption.
Image Mount can be helpful, but it is possible that images can be mounted but may not be bootable.
ImageManager Verification is essential in helping to prevent image rot. This test alerts the administrator that there is post-backup corruption, and the chain is possibly unusable.