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Product Environment 9-5
OnLine Features
Fault Tolerance and High Availability
OnLine uses several logging and recovery mechanisms to protect data
integrity and consistency in the event of an operating-system or media
failure. The data needed to support these logging and recovery mechanisms
are stored in the OnLine physical and logical logs, on archive tape, and on
logical log backup tape.
OnLine fault-tolerant features are enhanced by associated high-availability
features. You can create the archive tapes and the logical log backup tapes
while users are accessing OnLine. You can also use online archiving to create
incremental archives. Incremental archiving enables you to only back up data
that has changed since the last archive, which reduces the amount of time
required for archiving.
For more information about archive administration, refer to page 3-43. For
more information about logical log administration, refer to page 3-13. For
more information about using archive tapes and logical log backup tapes to
restore your data, refer to page 4-45. For more information about automatic
fast recovery in the event of an uncontrolled shutdown, refer to page 4-39.
In addition, OnLine supports mirroring, which can eliminate data loss as a
result of media (hardware) crashes. If a primary OnLine chunk becomes
unavailable for any reason, the mirror chunk is accessed immediately and, to
the user, transparently. For more information about OnLine mirroring, refer
to page 4-14.
Multimedia Support
OnLine supports two blob data types (TEXT and BYTE) with no practical
limit on the size of the data item stored. OnLine stores this blob data either
with other database data or in specially designated portions of the disk called
blobspaces. All OnLine fault-tolerant and high-availability features support
blob data. For more information about how OnLine stores blobs, refer to
page 2-144.