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I have heard that the Hitachi Data System's ShadowImage software can't work with Veritas Volume Manager. Is it true and if it is, what seems to be the problem?

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Veritas Volume Manager works fine with ShadowImage but mounting the shadow volume on the same server as production volume at the same time is generally not recommended. This IS possible through the "Command Control Interface" (CCI) "mount" command, but the mounting of image volumes is usually done on a separate server.

Storage based image copies are used for certain tasks. One reason for a "shadow image" to be created is for instant restore in case of production volume corruption. This would mean the production volume would be moved offline and the shadow then mounted as production. Another reason is for images to be created for "auto" mounting on a backup server. There are many other uses like breaking off a production image to be used on the decision support or reporting servers.

NT uses a disk "signature" which is recorded in the registry on all mounted volumes. An image volume since it is copied as an EXACT duplicate, would have the same disk signature and confuse the OS. This is where the CCI mount command comes into play, as it mounts the image as a different drive letter and "physical device" in the registry. The mount command can also mount the image automatically on a different server that is also running CCI, such as a backup server, so you can backup all your data without impacting production servers, during production hours.

One of the ShadowImage uses is for automatic server rollouts and upgrades. You boot into the SAN, install your new software version or update your application, then snap an image of that volume. You can then assign that image to other servers and reboot. Instant upgrade from NT to Win2K or rollout of new application version!

Chris

Editor's note: Do you agree with this expert's response? If you have more to share, post it in our Storage Networking discussion forum.

This was first published in March 2002

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