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Note that you must back up the cache with some type of battery so a power failure
doesn??™t result in the loss of data that was written to the cache, but hasn??™t yet been
destaged to the physical disk. Otherwise, data that Oracle assumes made it to disk
may be lost, thereby potentially corrupting the database. Figure 7-2 illustrates a database
server with a dedicated I/O subsystem.
Combined host-based and I/O subsystem volume management
In this configuration, disks are grouped into arrays within the I/O subsystem and
grouped again into coarser arrays using operating system volume management. On
EMC systems, for example, the physical disks are grouped into either RAID-1 mirrored
disk pairs or into a RAID-S striped configuration using four disks per stripe set.
166 | Chapter 7: Oracle Performance
(RAID-S is the term EMC [http://www.emc.com] uses for its specialized striping hardware
and software.)
Using EMC technology as an example, the operating system sees horizontal sections of
disk space across each RAID-1 disk or RAID-S array as single ???disks.


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