Subject: Re: Update section on NFS
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
 pgsql-docs <pgsql-docs@postgresql.org>
References: <e90f24bb-5423-6abb-58ec-501176eb4afc@2ndquadrant.com>
From: Joe Conway <mail@joeconway.com>
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Message-ID: <83a5bea3-57cd-e820-83eb-4a9c64082c19@joeconway.com>
Date: Tue, 23 Apr 2019 08:31:15 -0400
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From: Joe Conway <mail@joeconway.com>
To: Peter Eisentraut <peter.eisentraut@2ndquadrant.com>,
 pgsql-docs <pgsql-docs@postgresql.org>
Message-ID: <83a5bea3-57cd-e820-83eb-4a9c64082c19@joeconway.com>
Subject: Re: Update section on NFS
References: <e90f24bb-5423-6abb-58ec-501176eb4afc@2ndquadrant.com>
In-Reply-To: <e90f24bb-5423-6abb-58ec-501176eb4afc@2ndquadrant.com>

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On 4/23/19 6:10 AM, Peter Eisentraut wrote:
> Attached is a patch that rewrites the section on NFS.  The old section
> was ancient and didn't seem very helpful.
>=20
> AFAIK, the only strict requirement for using NFS with PostgreSQL is the=

> hard mount.  Anything else we should mention?
>=20
> I also reorganized the sectioning so that information about other file
> systems can be added more easily.

>     <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</produ=
ctname> does nothing
> -    special for <acronym>NFS</acronym> file systems, meaning it assume=
s
> -    <acronym>NFS</acronym> behaves exactly like locally-connected driv=
es.
> -    If the client or server <acronym>NFS</acronym> implementation does=
 not
> -    provide standard file system semantics, this can
> -    cause reliability problems (see <ulink
> -    url=3D"https://www.time-travellers.org/shane/papers/NFS_considered=
_harmful.html"></ulink>).
> -    Specifically, delayed (asynchronous) writes to the <acronym>NFS</a=
cronym>
> -    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.

<snip>

> +    <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 netwo=
rk
> +     problems, so this setup will require a careful monitoring setup. =
 (The
> +     <literal>soft</literal> option will interrupt system calls in cas=
e of
> +     network problems, but the <productname>PostgreSQL</productname> w=
ill not
> +     repeat system calls interrupted in this way, so any such interrup=
tion
> +     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 dri=
ves.
> +    </para>


Looks like you dropped the advice WRT the asynchronous mount option.
Isn't that is still relevant?


Joe

--=20
Crunchy Data - http://crunchydata.com
PostgreSQL Support for Secure Enterprises
Consulting, Training, & Open Source Development


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