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<p>Hello everyone,</p>
<p>I've tried just about everything the last weeks and my findings
are:</p>
<p>- the problem with LVM cache seems NOT to be caused by KVM/qemu.
But is <i>seems</i> that it is noticeable more inside a KVM. So
the slowdown of the cache also happens on HW-node, but you must
give it a serious go before you notice.</p>
<p>- Not a single time I succeeded in creating a well working cache
using LVM2 cache. In artificial / KVM setups and with <b>small</b>
devices it works (dm-testsuite etc). But in real life scenario
with <b>fully population all the PV's</b> on 2TB HDDs and 250G
SSDs (both RAID 1) the cache stopped working after 20 - 50 GB of
writes although the cache is 150+G large. Please use fio examples
below and always use new filenames so not the same blocks are
overwritten. <br>
</p>
<p>The poor performance stayed most of the time even when all blocks
were flushed. Very unpredictable cache performance / behavior.<br>
</p>
<p>I finally decided to go for dm-writeboost in stead of lvm2 cache
(dm-cache). This was the only way to create a well working cache
that works till 95% filled. But of course would be nicer to have
something that generally more stable like LVM2. <br>
</p>
<p>I guess in the sens of this mailing-list this issue is resolved
because it does not seem to belong here.<br>
</p>
<pre class="moz-signature" cols="72">--
Met vriendelijke groet,
Richard Landsman
<a class="moz-txt-link-freetext" href="http://rimote.nl">http://rimote.nl</a>
T: +31 (0)50 - 763 04 07
(ma-vr 9:00 tot 18:00)
24/7 bij storingen:
+31 (0)6 - 4388 7949
@RimoteSaS (Twitter Serviceberichten/security updates) </pre>
<div class="moz-cite-prefix">On 04/20/2017 04:23 PM, Sandro
Bonazzola wrote:<br>
</div>
<blockquote
cite="mid:CAPQRNTnMJvVukt98H6r0JEZ=ffWhuRM80FkTCpZCfdWayxpw9Q@mail.gmail.com"
type="cite">
<div dir="ltr"><br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Thu, Apr 20, 2017 at 12:32 PM,
Richard Landsman - Rimote <span dir="ltr"><<a
moz-do-not-send="true" href="mailto:richard@rimote.nl"
target="_blank">richard@rimote.nl</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
<div bgcolor="#FFFFFF">
<p>Hello everyone,</p>
<p>Anybody had the chance to test out this setup and
reproduce the problem? I assumed it would be something
that's used often these days and a solution would
benefit a lot of users. If can be of any assistance
please contact me. <br>
</p>
</div>
</blockquote>
<div><span style="font-size:12.8px">I haven't seen any
additional report of this happening, can you please try
to reproduce with the new qemu-kvm-ev-2.6.0-28.el7_</span><span
style="font-size:12.8px">3<wbr>.9.1 currently in
testing?</span> </div>
<blockquote class="gmail_quote" style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex">
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<p> </p>
<span class="m_-3432995202089825862gmail-">
<pre class="m_-3432995202089825862gmail-m_4322563754076754401moz-signature" cols="72">--
Met vriendelijke groet,
Richard Landsman
<a moz-do-not-send="true" class="m_-3432995202089825862gmail-m_4322563754076754401moz-txt-link-freetext" href="http://rimote.nl" target="_blank">http://rimote.nl</a>
T: +31 (0)50 - 763 04 07
(ma-vr 9:00 tot 18:00)
24/7 bij storingen:
+31 (0)6 - 4388 7949
@RimoteSaS (Twitter Serviceberichten/security updates) </pre>
</span></div>
<br>
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