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From: Greg Sabino Mullane <htamfids@gmail.com>
Date: Mon, 11 Aug 2025 12:41:12 -0400
Message-ID: <CAKAnmmLnSxW6ER0AXn9GxfL=84RWcei_7q2bPwieNyM+SS6mTQ@mail.gmail.com>
Subject: Re: Backups with filesystem snapshots
To: Nick Cleaton <nick@cleaton.net>
Cc: PostgreSQL General <pgsql-general@lists.postgresql.org>
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On Mon, Aug 11, 2025 at 9:01=E2=80=AFAM Nick Cleaton <nick@cleaton.net> wro=
te:

> If I take an instantaneous filesystem-level snapshot of the postgres
> data directory underneath a running postgres server, is that a safe
> backup without doing any pg_start_backup/pg_stop_backup ?
>

Safe, yes[*], but not particularly recommended except for special cases,
like spinning up a fast QA cluster. For backups, use a Postgres-aware
battle tested system like pgBackRest that offers more flexibility and more
safeguards.

* Assuming your hardware/OS drivers are being honest with you about fsync

starting up from that snapshot should look the same as recovering from an
> unclean postgres shutdown
> due to a kernel panic.
>

Yes, for all practical purposes it would be identical. Technically more
similar to pulling the plug on the server. :)

Cheers,
Greg

--
Crunchy Data - https://www.crunchydata.com
Enterprise Postgres Software Products & Tech Support

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<div dir=3D"ltr"><div dir=3D"ltr">On Mon, Aug 11, 2025 at 9:01=E2=80=AFAM N=
ick Cleaton &lt;<a href=3D"mailto:nick@cleaton.net">nick@cleaton.net</a>&gt=
; wrote:</div><div class=3D"gmail_quote gmail_quote_container"><blockquote =
class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-left:1px sol=
id rgb(204,204,204);padding-left:1ex">If I take an instantaneous filesystem=
-level snapshot of the postgres<br>
data directory underneath a running postgres server, is that a safe<br>
backup without doing any pg_start_backup/pg_stop_backup ?<br></blockquote><=
div><br></div><div>Safe, yes[*], but not particularly=C2=A0recommended exce=
pt for special cases, like spinning up a fast QA cluster. For backups, use =
a Postgres-aware battle tested system like pgBackRest that offers more flex=
ibility and more safeguards.</div><div><br></div><div>* Assuming your hardw=
are/OS drivers are being honest with you about fsync</div><div><br></div><b=
lockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;border-le=
ft:1px solid rgb(204,204,204);padding-left:1ex">starting up from that snaps=
hot should look the same as recovering from an unclean postgres shutdown<br=
>
due to a kernel panic.<br></blockquote><div><br></div><div>Yes, for all pra=
ctical purposes it would be identical. Technically more similar to pulling =
the plug on the server. :)</div><div><br></div><div>Cheers,</div></div><div=
 dir=3D"ltr" class=3D"gmail_signature"><div dir=3D"ltr"><div>Greg</div><div=
><br></div><div>--</div><div>Crunchy Data - <a href=3D"https://www.crunchyd=
ata.com" target=3D"_blank">https://www.crunchydata.com</a></div><div>Enterp=
rise Postgres Software Products &amp; Tech Support</div><div><br></div></di=
v></div></div>

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