Business Continuity Although backups are sufficient for most sites, enterprise sites that cannot afford to lose any data or suffer any downtime need to implement business continuity solutions, such as remote mirroring or electronic vaulting.Mirroring solutions are extremely expensive to implement because a high-throughput network link with low latency must be set up between the mirrored pair to maintain synchronous communication. Because of these stringent guidelines, leased lines are almost always required between non-co-located mirrored pairs. EMC Corp. offers a powerful system known as SRDF (Symmetrix Remote Data Facility), which provides real-time replication between EMC storage units. A top-of-the-line enterprise mirroring solution, SRDF pricing starts at $22,500. A less expensive alternative to remote mirroring is electronic vaulting. With electronic vaulting products such as DoubleTake from NSI Software, information about transactions is written into log files; these files are then forwarded to the backup site every few hours. Since electronic vaulting is an asynchronous form of communication, bandwidth and latency requirements are far less stringent than with mirroring. Typical IP-based networks are suitable as a replication line, for example, which vastly reduces the cost of implementation compared with mirroring solutions. The downside to vaulting is that if a primary site is lost, transactions that have not been forwarded to the backup site could be lost, as would incomplete transactions.
To protect key databases, Bronson uses multiple data mirrors to limit downtime. "On the system on which we run our production instance of Oracle Financials, we mirror three disk arrays," he said. "We disassociate one array at night, then perform an offline backup of that array and reassociate after the backup is complete. Our downtime is about 15 minutes during the 24-hour period while we shut down the database."