I moved from tape backups to backup-to-disk via 1gb ethernet. I have an exchange DB of 21GB which backs up in 15 minutes with verification. (Full Online Exchange DB backup. Symantec BE10d)

My exchange server is a Dell PowerEdge 2850, Raid5, reduntant power/internal fans, UPS and generator backup.

You can also do the incremental backups which will just backup the transaction logs (careful of circular logging if you do this). That would be a quicker backup. Then a full backup would bring the log file data into your main database(s).
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let the wise listen and add to their learning,
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