9:41 a.m.
This is a multi-part message in MIME format.
--------------E1421BB04F7A8066E3169AB1
Content-Type: text/plain; charset=utf-8; format=flowed
Content-Transfer-Encoding: 7bit
Ok, great, thanks for the clarification.
Therefore a replica 3 configuration means raw storage space cost is
'similar' to a RAID 1 and actual data exists only 2 times and two
different servers.
Regards
Fernando
On 24/04/2017 11:35, Denis Chaplygin wrote:
With arbiter volume you still have a replica 3 volume, meaning that
you have three participants in your quorum. But only two of those
participants keep the actual data. Third one, the arbiter, stores only
some metadata, not the files content, so data is not replicated 3 times.
On Mon, Apr 24, 2017 at 3:33 PM, FERNANDO FREDIANI
<fernando.frediani(a)upx.com <mailto:fernando.frediani@upx.com>> wrote:
But then quorum doesn't replicate data 3 times, does it ?
Fernando
On 24/04/2017 10:24, Denis Chaplygin wrote:
> Hello!
>
> On Mon, Apr 24, 2017 at 3:02 PM, FERNANDO FREDIANI
> <fernando.frediani(a)upx.com <mailto:fernando.frediani@upx.com>>
wrote:
>
> Out of curiosity, why do you and people in general use more
> replica 3 than replica 2 ?
>
>
> The answer is simple - quorum. With just two participants you
> don't know what to do, when your peer is unreachable. When you
> have three participants, you are able to establish a majority. In
> that case, when two partiticipants are able to communicate, they
> now, that lesser part of cluster knows, that it should not accept
> any changes.
>
> If I understand correctly this seems overkill and waste of
> storage as 2 copies of data (replica 2) seems pretty
> reasonable similar to RAID 1 and still in the worst case the
> data can be replicated after a fail. I see that replica 3
> helps more on performance at the cost of space.
>
>
> You are absolutely right. You need two copies of data to provide
> data redundancy and you need three (or more) members in cluster
> to provide distinguishable majority. Therefore we have arbiter
> volumes, thus solving that issue [1].
>
> [1]
>
https://gluster.readthedocs.io/en/latest/Administrator%20Guide/arbiter-vo...
>
<https://gluster.readthedocs.io/en/latest/Administrator%20Guide/arbiter-vo...
--------------E1421BB04F7A8066E3169AB1
Content-Type: text/html; charset=utf-8
Content-Transfer-Encoding: 8bit
<html>
<head>
<meta content="text/html; charset=utf-8"
http-equiv="Content-Type">
</head>
<body bgcolor="#FFFFFF" text="#000000">
<p>Ok, great, thanks for the clarification.</p>
<p>Therefore a replica 3 configuration means raw storage space cost
is 'similar' to a RAID 1 and actual data exists only 2 times and
two different servers.</p>
<p>Regards<br>
Fernando<br>
</p>
<br>
<div class="moz-cite-prefix">On 24/04/2017 11:35, Denis Chaplygin
wrote:<br>
</div>
<blockquote
cite="mid:CANVzE5nokh4MnXYfh8-oSQ8v0o1R4cKP0q1k5SKWPBqBHXiVqg@mail.gmail.com"
type="cite">
<div dir="ltr">With arbiter volume you still have a replica 3
volume, meaning that you have three participants in your quorum.
But only two of those participants keep the actual data. Third
one, the arbiter, stores only some metadata, not the files
content, so data is not replicated 3 times.<br>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Apr 24, 2017 at 3:33 PM,
FERNANDO FREDIANI <span dir="ltr"><<a
moz-do-not-send="true"
href="mailto:fernando.frediani@upx.com"
target="_blank">fernando.frediani(a)upx.com</a>&gt;</span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<p>But then quorum doesn't replicate data 3 times, does it
?</p>
<span class="HOEnZb"><font color="#888888">
<p>Fernando<br>
</p>
</font></span>
<div>
<div class="h5"> <br>
<div class="m_-3736559709896304842moz-cite-prefix">On
24/04/2017 10:24, Denis Chaplygin wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Hello!<br>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Mon, Apr 24, 2017 at
3:02 PM, FERNANDO FREDIANI <span
dir="ltr"><<a
moz-do-not-send="true"
href="mailto:fernando.frediani@upx.com"
target="_blank">fernando.frediani(a)upx.com</a>&gt;</span>
wrote:<br>
<blockquote style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex"
class="gmail_quote">
<div bgcolor="#FFFFFF">Out of curiosity, why
do you and people in general use more
replica 3 than replica 2 ? </div>
</blockquote>
<div><br>
</div>
<div>The answer is simple - quorum. With just
two participants you don't know what to do,
when your peer is unreachable. When you have
three participants, you are able to
establish a majority. In that case, when two
partiticipants are able to communicate, they
now, that lesser part of cluster knows, that
it should not accept any changes.<br>
</div>
<div> </div>
<blockquote style="margin:0px 0px 0px
0.8ex;border-left:1px solid
rgb(204,204,204);padding-left:1ex"
class="gmail_quote">
<div bgcolor="#FFFFFF">
<p>If I understand correctly this seems
overkill and waste of storage as 2
copies of data (replica 2) seems pretty
reasonable similar to RAID 1 and still
in the worst case the data can be
replicated after a fail. I see that
replica 3 helps more on performance at
the cost of space.</p>
<span
class="m_-3736559709896304842gmail-HOEnZb"></span><br>
</div>
</blockquote>
</div>
You are absolutely right. You need two copies of
data to provide data redundancy and you need
three (or more) members in cluster to provide
distinguishable majority. Therefore we have
arbiter volumes, thus solving that issue [1]. <br>
<br>
[1] <a moz-do-not-send="true"
href="https://gluster.readthedocs.io/en/latest/Administrator%20Guide/arbiter-volumes-and-quorum/"
target="_blank">https://gluster.readthedocs.<wbr>io/en/latest/Administrator%<wbr>20Guide/arbiter-volumes-and-<wbr>quorum/</a><br>
</div>
</div>
</blockquote>
<br>
</div>
</div>
</div>
</blockquote>
</div>
<br>
</div>
</blockquote>
<br>
</body>
</html>
--------------E1421BB04F7A8066E3169AB1--