System Fault Tolerance

(SFT) A means of protecting data by providing procedures that allow you to automatically recover from hardware failures.

There are three levels of SFT; each level of redundancy (duplication) decreases the possibility of data loss.

• SFT Level I: Hot Fix. This is generally operating system dependent, and ensures that data is not saved to faulty blocks on the server’s hard disk.
• SFT Level II: Disk Mirroring or Duplexing. Disk mirroring protects against hard disk failures by pairing two hard disks on the same channel. The disks operate in tandem, constantly storing and updating the same files. Disk duplexing pairs two disks on different channels, which protects data from the failure of the hard disk or the channel that joins the hard disk to the server.
• SFT Level III: Server Mirroring. Provides protection from server failure with a secondary, identical server that immediately takes over network operations when the primary server fails.

Each level of SFT protection includes the previous levels; that is, SFT III includes level I and level II protection.

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