Pulling an image of your storage server is a real help both in terms of deploying new servers and in disaster recovery on existing ones. However not all imaging products are created equal.
According to L. D. Weller, a senior product manager at Symantec, there are really two kinds of imaging products available in the windows environment, sharply delineated according to their use and performance. The more common class are products like Norton Ghost from Symantec and Deploy Center, originally from PowerQuest, but acquired by Symantec in its recent acquisition of PowerQuest.
According to Weller, these are often 16-bit Windows products which are designed more for deployment or partial restoration than disaster recovery and assume that the operating system on the target server is functioning.
The other class are products which are designed to restore everything, operating system and all. This includes PowerQuest's (now Symantec) V2I Protector at the low end, up through products
like EMC's Snapview at the higher end. All these products work by creating an image of everything, including the OS. While these products are not replacements for archival backup, they can offer much faster restoration than technologies such as tape and they can be used with a remote server, a local server, or even another partition on system being protected.
Image products in this class vary considerably in their sophistication and ease of use, generally trading one for the other. Symantec's V2I is designed to be as easy to use as possible and is best used in workgroups or small enterprises. Products like Snapview are more complex to configure and design...
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ed to protect large enterprises.
Weller has several suggestions for anyone who wants to use an image product for disaster recovery. "Step one is to determine how critical the data is and where it will be stored. Do you want to put it on a local partition, a NAS box, a RAID array, where?" Weller said. "Step two is based on the amount of storage you have decide what kind of policy you're going to set in terms
of images. How often are you going to take incremental captures?"
One issue that arises in discussing images for disaster recovery is how often to make an incremental image. For Weller this is largely a non-issue. "The more frequently you take it, the smaller the incremental image," Weller said. "You're not really wasting that much space by having frequent incrementals and you don't take that much of a performance hit." However he says you do need to keep track of how many old images you keep. "If you don't delete the old images they add up pretty quickly," he said.
"The next step is to determine what kind of role the images will play in the archival process," Weller said. One option is to make your tape backups from the most recent image using tape attached either directly to the image storage device or over a SAN. Another way to use the images is to mount captured images as if they were a drive and perform operations like scanning for viruses or grabbing a file which has become corrupted.
About the author: Rick Cook has been writing about mass storage since the days when the term meant an 80K floppy disk. The computers he learned on used ferrite cores and magnetic drums. For the last twenty years he has been a freelance writer specializing in storage and other computer issues.
