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<chapter id="backup">

<title>Backup and Restore</title>

</para>

<para>

If your database is spread across multiple volumes (for example,

if you are using tablespaces) there may not be any way

to obtain exactly-simultaneous frozen snapshots of all the volumes.

If your database is spread across multiple file systems there may not

be any way to obtain exactly-simultaneous frozen snapshots of all

the volumes. For example, if your data files and WAL log on different

file disks, or if tablespaces are on different file systems, it might

not be possible to use snapshots because the snapshots must be simultaneous.

Read your file system documentation very carefully before trusting

to the consistent-snapshot technique in such situations. The safest

approach is to shut down the database server for long enough to

<para>

Another option is to use <application>rsync</> to perform a file

system backup. First, while the database server is running,

run <application>rsync</>, then shut down the database

server and perform a second <application>rsync</>, then

restart the database server. This allows a file system backup to be

performed with minimal downtime.

system backup. This is done by first running <application>rsync</>

while the database server is running, then shutting down the database

server just long enough to do a second <application>rsync</>. The

second <application>rsync</> will be much quicker than the first,

but will be consistent because the server was down. This method

allows a file system backup to be performed with minimal downtime.

</para>

<para>