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<chapter id="high-availability">

<title>High Availability and Load Balancing</title>

disk array fails or becomes corrupt, the primary and standby

servers are both nonfunctional. Another issue is that the

standby server should never access the shared storage while

the primary server is running. It is also possible to use

some type of file system mirroring to keep the standby server

current, but the mirroring must be done in a way that ensures the

standby server has a consistent copy of the file system.

the primary server is running.

</para>

<para>

A modified version of shared hardware functionality is file system

replication, where all changes to a file system are mirrored to a file

system residing on another computer. The only restriction is that

the mirroring must be done in a way that ensures the standby server

has a consistent copy of the file system &mdash; specifically, writes

to the standby must be done in the same order as those on the master.

DRBD is a popular file system replication solution for Linux.

</para>

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