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In-Reply-To: <1438f48b-0a6d-4fb7-92dc-3688251e0a00@assyoma.it>
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From: Mark Mielke <mark.mielke@gmail.com>
Date: Fri, 7 Apr 2017 04:19:24 -0400
Message-ID: <CALm7yL2N1Gs+ry+vkJucuYxXeGua3LpWCR+CEy_Zdgq-w-A3ag@mail.gmail.com>
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Subject: Re: [linux-lvm] Snapshot behavior on classic LVM vs ThinLVM
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On Thu, Apr 6, 2017 at 10:31 AM, Gionatan Danti <g.danti@assyoma.it> wrote:

> I'm seeking some advice for a new virtualization system (KVM) on top of
> LVM. The goal is to take agentless backups via LVM snapshots.
>
> In short: what you suggest to snapshot a quite big (8+ TB) volume? Classic
> LVM (with old snapshot behavior) or thinlvm (and its new snapshot method)?
>

I found classic LVM snapshots to suffer terrible performance. I switched to
BTRFS as a result, until LVM thin pools became a real thing, and I happily
switched back.

I expect this depends on exactly what access patterns you have, how many
accesses will happen during the time the snapshot is held, and whether you
are using spindles or flash. Still, even with some attempt to be objective
and critical... I think I would basically never use classic LVM snapshots
for any purpose, ever.


-- 
Mark Mielke <mark.mielke@gmail.com>

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<div dir=3D"ltr"><div class=3D"gmail_extra"><div class=3D"gmail_quote">On T=
hu, Apr 6, 2017 at 10:31 AM, Gionatan Danti <span dir=3D"ltr">&lt;<a href=
=3D"mailto:g.danti@assyoma.it" target=3D"_blank">g.danti@assyoma.it</a>&gt;=
</span> wrote:<br><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px=
 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex">I&#39;m=
 seeking some advice for a new virtualization system (KVM) on top of LVM. T=
he goal is to take agentless backups via LVM snapshots.<br>
<br>
In short: what you suggest to snapshot a quite big (8+ TB) volume? Classic =
LVM (with old snapshot behavior) or thinlvm (and its new snapshot method)?<=
br></blockquote><div><br></div>I found classic LVM snapshots to suffer terr=
ible performance. I switched to BTRFS as a result, until LVM thin pools bec=
ame a real thing, and I happily switched back.</div><div class=3D"gmail_quo=
te"><br></div><div class=3D"gmail_quote">I expect this depends on exactly w=
hat access patterns you have, how many accesses will happen during the time=
 the snapshot is held, and whether you are using spindles or flash. Still, =
even with some attempt to be objective and critical... I think I would basi=
cally never use classic LVM snapshots for any purpose, ever.</div><br clear=
=3D"all"><div><br></div>-- <br><div class=3D"gmail_signature">Mark Mielke &=
lt;<a href=3D"mailto:mark.mielke@gmail.com" target=3D"_blank">mark.mielke@g=
mail.com</a>&gt;<br><br></div>
</div></div>

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