Consider mirroring for critical data components

Consider mirroring for the dbspaces that contain critical data. Mirroring these dbspaces ensures that the database server can continue to operate even when a single disk fails.

However, depending on the mix of I/O requests for a given dbspace, a trade-off exists between the fault tolerance of mirroring and I/O performance. You obtain a marked performance advantage when you mirror dbspaces that have a read-intensive usage pattern and a slight performance disadvantage when you mirror write-intensive dbspaces.

Most modern storage devices have excellent mirroring capabilities, and you can use those devices instead of the mirroring capabilities of the database server.

When mirroring is in effect, two disks are available to handle read requests, and the database server can process a higher volume of those requests. However, each write request requires two physical write operations and does not complete until both physical operations are performed. The write operations are performed in parallel, but the request does not complete until the slower of the two disks performs the update. Thus, you experience a slight performance penalty when you mirror write-intensive dbspaces.

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