Date: Fri, 10 Jan 2025 14:01:26 -0500 From: Karl Denninger <karl@denninger.net> To: freebsd-fs@freebsd.org Subject: Re: How can I tell when ZFS has finished creating a snapshot? Message-ID: <44c10641-8f1b-476f-ba5b-29d4a5f28c9c@denninger.net> In-Reply-To: <alpine.BSF.2.22.395.2501101830270.43509@mail0.time-domain.net> References: <alpine.BSF.2.22.395.2501101830270.43509@mail0.time-domain.net>
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<p><br>
</p>
<div class=3D"moz-cite-prefix">On 1/10/2025 1:52 PM, andy thomas
wrote:<br>
</div>
<blockquote type=3D"cite"
cite=3D"mid:alpine.BSF.2.22.395.2501101830270.43509@mail0.time-domain.net=
">Is
there any way I can find out when a ZFS snapshot has completed and
can be used, say, for replicating to another server?
<br>
<br>
Using the 'zfs snapshot -r ...' command, the command prompt
re-appears almost immediately suggesting the command has completed
and using the 'zfs list -t snapshot' command the 'USED' column
will initially report zero and then it will slowly grow over the
next few hours. But it seems to take a long time with no
zfs-related processes being reported by 'ps ax'. For example,
after 3 hours, a snapshot of a 80TB raidz1 pool with only a little
over 3 TB used has reported 17.4MB used:
<br>
<br>
=C2=A0=C2=A0=C2=A0=C2=A0NAME=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=
=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=
=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 USED=C2=A0 A=
VAIL=C2=A0 REFER=C2=A0
MOUNTPOINT
<br>
=C2=A0=C2=A0=C2=A0=C2=A0<a class=3D"moz-txt-link-abbreviated" href=3D=
"mailto:clustor2/ma@2025-01-10_14.45.00">clustor2/ma@2025-01-10_14.45.00<=
/a>=C2=A0 17.4M=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 -=C2=A0 3.09T=C2=A0 -
<br>
<br>
but over the next hour, this 17.4MB usage figure has not increased
at all. So I don't know whether to wait another few hours before
using 'zfs send' or 'zxfer' to copy the snapshot to a backup
server, or whether the snapshot has in fact finished.
<br>
<br>
Is there a way to find out the status of a snapshot creation?
<br>
<br>
Thanks in advance for any suggestions,
<br>
</blockquote>
<p>The snapshot is complete when the command returns -- within the
filesystem a snapshot is an atomic operation.<br>
</p>
<p><i>Once made all writes to that filesystem are copy-on-write </i>s=
o
as time goes on the "Used" amount increases (and the free space
goes down by an equal amount) because each block that is modified
(and only that block) is copied.</p>
<div class=3D"moz-signature">-- <br>
Karl Denninger<br>
<a href=3D"mailto:karl@denninger.net" class=3D"moz-txt-link-freetex=
t">karl@denninger.net</a><br>
<i>The Market Ticker</i><br>
<font size=3D"-2"><i>[S/MIME encrypted email preferred]</i></font><=
/div>
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