Attached is a patch that rewrites the section on NFS. The old section
was ancient and didn't seem very helpful.
AFAIK, the only strict requirement for using NFS with PostgreSQL is the
hard mount. Anything else we should mention?
I also reorganized the sectioning so that information about other file
systems can be added more easily.
Can anyone suggest some succinct advice on what file systems are
supported on Windows (see XXX in the patch)?
--
Peter Eisentraut http://www.2ndQuadrant.com/
PostgreSQL Development, 24x7 Support, Remote DBA, Training & Services
From 6b9430b395997955be718244d0061eceb1319a9e Mon Sep 17 00:00:00 2001
From: Peter Eisentraut <pe...@eisentraut.org>
Date: Tue, 23 Apr 2019 12:03:57 +0200
Subject: [PATCH] doc: Update section on NFS
---
doc/src/sgml/runtime.sgml | 71 ++++++++++++++++++++++-----------------
1 file changed, 40 insertions(+), 31 deletions(-)
diff --git a/doc/src/sgml/runtime.sgml b/doc/src/sgml/runtime.sgml
index 388dc7e966..7c76f5b8aa 100644
--- a/doc/src/sgml/runtime.sgml
+++ b/doc/src/sgml/runtime.sgml
@@ -229,42 +229,51 @@ <title>Use of Secondary File Systems</title>
</sect2>
- <sect2 id="creating-cluster-nfs">
- <title>Use of Network File Systems</title>
-
- <indexterm zone="creating-cluster-nfs">
- <primary>Network File Systems</primary>
- </indexterm>
- <indexterm><primary><acronym>NFS</acronym></primary><see>Network File
Systems</see></indexterm>
- <indexterm><primary>Network Attached Storage
(<acronym>NAS</acronym>)</primary><see>Network File Systems</see></indexterm>
+ <sect2 id="creating-cluster-filesystem">
+ <title>File Systems</title>
<para>
- Many installations create their database clusters on network file
- systems. Sometimes this is done via <acronym>NFS</acronym>, or by using a
- Network Attached Storage (<acronym>NAS</acronym>) device that uses
- <acronym>NFS</acronym> internally. <productname>PostgreSQL</productname>
does nothing
- special for <acronym>NFS</acronym> file systems, meaning it assumes
- <acronym>NFS</acronym> behaves exactly like locally-connected drives.
- If the client or server <acronym>NFS</acronym> implementation does not
- provide standard file system semantics, this can
- cause reliability problems (see <ulink
-
url="https://www.time-travellers.org/shane/papers/NFS_considered_harmful.html";></ulink>).
- Specifically, delayed (asynchronous) writes to the <acronym>NFS</acronym>
- server can cause data corruption problems. If possible, mount the
- <acronym>NFS</acronym> file system synchronously (without caching) to avoid
- this hazard. Also, soft-mounting the <acronym>NFS</acronym> file system is
- not recommended.
+ Generally, any file system with POSIX semantics can be used for
+ PostgreSQL. (On Windows, all standard Windows file systems are
+ supported. XXX?) Users prefer different file systems for a variety of
+ reasons, including vendor support, performance, and familiarity.
+ Experience suggests that, all other things being equal, one should not
+ expect major performance or behavior changes merely from switching file
+ systems or making minor file system configuration changes.
</para>
- <para>
- Storage Area Networks (<acronym>SAN</acronym>) typically use communication
- protocols other than <acronym>NFS</acronym>, and may or may not be subject
- to hazards of this sort. It's advisable to consult the vendor's
- documentation concerning data consistency guarantees.
- <productname>PostgreSQL</productname> cannot be more reliable than
- the file system it's using.
- </para>
+ <sect3 id="creating-cluster-nfs">
+ <title>NFS</title>
+
+ <indexterm zone="creating-cluster-nfs">
+ <primary>NFS</primary>
+ </indexterm>
+ <para>
+ It is possible to use an NFS file system for storing the
+ <productname>PostgreSQL</productname> data directory. The only
+ requirement is that the file system is mounted using the
+ <literal>hard</literal> option. With the <literal>hard</literal> option,
+ processes can <quote>hang</quote> indefinitely if there are network
+ problems, so this setup will require a careful monitoring setup. (The
+ <literal>soft</literal> option will interrupt system calls in case of
+ network problems, but the <productname>PostgreSQL</productname> will not
+ repeat system calls interrupted in this way, so any such interruption
+ will result in an I/O error being reported.)
+ <productname>PostgreSQL</productname> does nothing special for
+ <acronym>NFS</acronym> file systems, meaning it assumes
+ <acronym>NFS</acronym> behaves exactly like locally-connected drives.
+ </para>
+
+ <para>
+ In some cases, an external storage product can be accessed either via NFS
+ or a lower-level protocol such as iSCSI. In the latter case, the storage
+ appears as a block device and any available file system can be created on
+ it. That approach might relieve the DBA from having to deal with some of
+ the idiosyncrasies of NFS, but of course the complexity of managing
+ remote storage then happens at other levels.
+ </para>
+ </sect3>
</sect2>
</sect1>
--
2.21.0
