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Unix Backup and Recovery by W. Curtis Preston

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Physical Backups Without a Storage Manager

Tip

The following section covers physical backups. If you are unfamiliar with these terms, please consult Chapter 13.

There are a number of third-party backup utilities that can aid in the backup of Sybase databases, but because of their expense, not every site can afford them for all data servers. Even if you have a backup application, you may not want to spend several thousand dollars per server for the Sybase interface. Because Sybase was developed before many of these utilities, there are methods that can be used to back up a Sybase server at a fraction of the cost and with a fair amount of stability and uniformity. These methods include backups directly to both disk and tape.

Sybase databases can reside on both cooked filesystem files and raw disk devices. Sybase recommends not using the filesystem because of the delay caused by the I/O caching. When Sybase writes out data to disk, it assumes the data is written to disk immediately. When using a filesystem-based database, the operating system first writes the data to a memory cache and then at a later point the data is written to disk. Because Sybase writes out changed data pages to disk along with a transaction log entry during transaction processing, if there is a delay in writing out the pages and a problem occurs, not all the data and transaction pages would be written out. This could leave the database with changed pages, no record in the transaction log, and a partially completed ...

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