Recovering from a data center disaster


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Making the best of tape
Two variables will affect reaching a "ready to recover" state with tape. First, how long are tapes kept at the recovery site before being moved to an off-site vendor? And were your backup servers and their indexes located local to your primary data center and thus destroyed by the disaster, or were they located at your recovery site?

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Disk-only approach yields fastest time to recovery

Because technology allows us to access a library's robotic arm from across a wide distance, a storage area network (SAN) designer has the option of locating the backup server at either location. But for security reasons, an organization may not want a server that has access to every other client network to remain in a less-secure location. If there's any way to lighten the fears of the security organization in your company by enhancing the security at the remote location and in your network, then perhaps you should explore those paths.

One huge benefit you would realize is not having to rebuild your backup server from scratch because it was at a safe distance at the time of the disaster. This saves you time by not requiring you to restore your backup server's indexes, as well as keeping those indexes available to you for report queries. With the indexes available, you can execute prewritten scripts to query the backup server for the tape volumes that will be necessary to restore a backup client to a particular recovery time and then load those tapes as they arrive from the off-site vendor. However, this benefit can be fully exploited only when you have a priority list of application servers to restore.

The costs associated with a tape-based DR solution range from the procurement of tapes and their tape drives, to the management of the physical tape for the rest of the tape's life. Tape costs will vary depending on the technology used for backups. The choice of DLT, LTO, AIT or other midcartridge load technologies will depend on the number of backup clients that must be assigned to each tape library and the data characteristics of the clients.

For example, if you have a high number of clients with lots of mount points assigned to a tape library for backup, recovering that same high number of mount points implies a more significant amount of tape mounts, because mount points are assigned to specific tape drives during backups. A complete DR slows restores for all but the tape drives with the fastest of load and unload times. And because the capacity of the tapes associated with those types of tape drives are often much smaller than those built for capacity, more of them are necessary to regain the capacity lost to the mount speed of the tape drive. This adds cost to the tape-based solution by requiring more tapes, floor space and staff to administer a large-scale DR solution.

This was first published in August 2003

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