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<title>Berkeley DB Reference Guide: Remote filesystems</title>
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<td><h3><dl><dt>Berkeley DB Reference Guide:<dd>Environment</dl></h3></td>
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<h1 align=center>Remote filesystems</h1>
<p>When regions are backed by the filesystem, it is a common error to attempt
to create Berkeley DB environments backed by remote file systems such as the
Network File System (NFS) or the Andrew File System (AFS). Remote
filesystems rarely support mapping files into process memory, and even
more rarely support correct semantics for mutexes after the attempt
succeeds. For this reason, we strongly recommend that the database
environment directory reside in a local filesystem.
<p>For remote file systems that do allow system files to be mapped into
process memory, home directories accessed via remote file systems cannot
be used simultaneously from multiple clients. None of the commercial
remote file systems available today implement coherent, distributed shared
memory for remote-mounted files. As a result, different machines will
see different versions of these shared regions and the system behavior is
undefined.
<p>Databases, log files and temporary files may be placed on remote
filesystems, <b>as long as the remote filesystem fully supports
standard POSIX filesystem semantics</b>, although the application may incur
a performance penalty for doing so. Obviously, NFS-mounted databases
cannot be accessed from more than one Berkeley DB environment (and therefore
from more than one system), at a time since no Berkeley DB database may be
accessed from more than one Berkeley DB environment at a time.
<p><dl compact>
<p><dt>Linux note:<dd>Some Linux releases are known to not support complete semantics for the
POSIX fsync call on NFS-mounted filesystems. No Berkeley DB files should be
placed on NFS-mounted filesystems on these systems.
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