<div dir="ltr"><br><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Aug 8, 2017 at 12:03 AM, FERNANDO FREDIANI <span dir="ltr"><<a href="mailto:fernando.frediani@upx.com" target="_blank">fernando.frediani@upx.com</a>></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>Thanks for the detailed answer Erekle.</p>
<p>I conclude that it is worth in any scenario to have a arbiter
node in order to avoid wasting more disk space to RAID X + Gluster
Replication on the top of it. The cost seems much lower if you
consider running costs of the whole storage and compare it with
the cost to build the arbiter node. Even having a fully redundant
arbiter service with 2 nodes would make it wort on a larger
deployment.</p></div></blockquote><div><br></div><div><br></div><div>Note that although you get the same consistency as a replica 3 setup, a 2+arbiter gives you data availability as a replica 2 setup. May or may not be OK with your high availability requirements.</div><div>Y.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div bgcolor="#FFFFFF" text="#000000">
<p>Regards<span class="HOEnZb"><font color="#888888"><br>
Fernando</font></span></p><div><div class="h5">
<div class="m_523492013473682272moz-cite-prefix">On 07/08/2017 17:07, Erekle Magradze
wrote:<br>
</div>
<blockquote type="cite">
<p>Hi Fernando (sorry for misspelling your name, I used a
different keyboard),</p>
<p>So let's go with the following scenarios:</p>
<p>1. Let's say you have two servers (replication factor is 2),
i.e. two bricks per volume, in this case it is strongly
recommended to have the arbiter node, the metadata storage that
will guarantee avoiding the split brain situation, in this case
for arbiter you don't even need a disk with lots of space, it's
enough to have a tiny ssd but hosted on a separate server.
Advantage of such setup is that you don't need the RAID 1 for
each brick, you have the metadata information stored in arbiter
node and brick replacement is easy.</p>
<p>2. If you have odd number of bricks (let's say 3, i.e.
replication factor is 3) in your volume and you didn't create
the arbiter node as well as you didn't configure the quorum, in
this case the entire load for keeping the consistency of the
volume resides on all 3 servers, each of them is important and
each brick contains key information, they need to cross-check
each other (that's what people usually do with the first try of
gluster :) ), in this case replacing a brick is a big pain and
in this case RAID 1 is a good option to have (that's the
disadvantage, i.e. loosing the space and not having the JBOD
option) advantage is that you don't have the to have additional
arbiter node.</p>
<p>3. You have odd number of bricks and configured arbiter node,
in this case you can easily go with JBOD, however a good
practice would be to have a RAID 1 for arbiter disks (tiny 128GB
SSD-s ar perfectly sufficient for volumes with 10s of TB-s in
size.)</p>
<p>That's basically it</p>
<p>The rest about the reliability and setup scenarios you can find
in gluster documentation, especially look for quorum and arbiter
node configs+options.</p>
<p>Cheers</p>
<p>Erekle</p>
P.S. What I was mentioning, regarding a good practice is mostly
related to the operations of gluster not installation or
deployment, i.e. not the conceptual understanding of gluster
(conceptually it's a JBOD system).<br>
<br>
<div class="m_523492013473682272moz-cite-prefix">On 08/07/2017 05:41 PM, FERNANDO
FREDIANI wrote:<br>
</div>
<blockquote type="cite">
<p>Thanks for the clarification Erekle.</p>
<p>However I get surprised with this way of operating from
GlusterFS as it adds another layer of complexity to the system
(either a hardware or software RAID) before the gluster config
and increase the system's overall costs.<br>
</p>
<p>An important point to consider is: In RAID configuration you
already have space 'wasted' in order to build redundancy
(either RAID 1, 5, or 6). Then when you have GlusterFS on the
top of several RAIDs you have again more data replicated so
you end up with the same data consuming more space in a group
of disks and again on the top of several RAIDs depending on
the Gluster configuration you have (in a RAID 1 config the
same data is replicated 4 times).</p>
<p>Yet another downside of having a RAID (specially RAID 5 or 6)
is that it reduces considerably the write speeds as each group
of disks will end up having the write speed of a single disk
as all other disks of that group have to wait for each other
to write as well.<br>
</p>
<p>Therefore if Gluster already replicates data why does it
create this big pain you mentioned if the data is replicated
somewhere else, can still be retrieved to both serve clients
and reconstruct the equivalent disk when it is replaced ?</p>
<p>Fernando<br>
</p>
<br>
<div class="m_523492013473682272moz-cite-prefix">On 07/08/2017 10:26, Erekle
Magradze wrote:<br>
</div>
<blockquote type="cite">
<p>Hi Frenando,</p>
<p>Here is my experience, if you consider a particular hard
drive as a brick for gluster volume and it dies, i.e. it
becomes not accessible it's a huge hassle to discard that
brick and exchange with another one, since gluster some
tries to access that broken brick and it's causing (at least
it cause for me) a big pain, therefore it's better to have a
RAID as brick, i.e. have RAID 1 (mirroring) for each brick,
in this case if the disk is down you can easily exchange it
and rebuild the RAID without going offline, i.e switching
off the volume doing brick manipulations and switching it
back on.<br>
</p>
<p>Cheers</p>
<p>Erekle<br>
</p>
<br>
<div class="m_523492013473682272moz-cite-prefix">On 08/07/2017 03:04 PM, FERNANDO
FREDIANI wrote:<br>
</div>
<blockquote type="cite">
<p>For any RAID 5 or 6 configuration I normally follow a
simple gold rule which gave good results so far:<br>
- up to 4 disks RAID 5<br>
- 5 or more disks RAID 6</p>
<p>However I didn't really understand well the
recommendation to use any RAID with GlusterFS. I always
thought that GlusteFS likes to work in JBOD mode and
control the disks (bricks) directlly so you can create
whatever distribution rule you wish, and if a single disk
fails you just replace it and which obviously have the
data replicated from another. The only downside of using
in this way is that the replication data will be flow
accross all servers but that is not much a big issue.</p>
<p>Anyone can elaborate about Using RAID + GlusterFS and
JBOD + GlusterFS.</p>
<p>Thanks<br>
Regards<br>
Fernando<br>
</p>
<br>
<div class="m_523492013473682272moz-cite-prefix">On 07/08/2017 03:46, Devin
Acosta wrote:<br>
</div>
<blockquote type="cite">
<div id="m_523492013473682272bloop_customfont" style="color:rgb(0,0,0);margin:0px"><font face="Input
Mono"><br>
</font></div>
<div id="m_523492013473682272bloop_customfont" style="color:rgb(0,0,0);margin:0px"><font face="Input
Mono">Moacir,</font></div>
<div id="m_523492013473682272bloop_customfont" style="color:rgb(0,0,0);margin:0px"><font face="Input
Mono"><br>
</font></div>
<div id="m_523492013473682272bloop_customfont" style="color:rgb(0,0,0);margin:0px"><font face="Input
Mono">I have recently installed multiple Red Hat
Virtualization hosts for several different companies,
and have dealt with the Red Hat Support Team in depth
about optimal configuration in regards to setting up
GlusterFS most efficiently and I wanted to share with
you what I learned.</font></div>
<div id="m_523492013473682272bloop_customfont" style="color:rgb(0,0,0);margin:0px"><font face="Input
Mono"><br>
</font></div>
<div id="m_523492013473682272bloop_customfont" style="color:rgb(0,0,0);margin:0px"><font face="Input
Mono">In general Red Hat Virtualization team frowns
upon using each DISK of the system as just a JBOD,
sure there is some protection by having the data
replicated, however, the recommendation is to use RAID
6 (preferred) or RAID-5, or at least RAID-1 at the
very least.</font></div>
<div id="m_523492013473682272bloop_customfont" style="color:rgb(0,0,0);margin:0px"><font face="Input
Mono"><br>
</font></div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><font face="Input Mono">Here is the direct quote from Red
Hat when I asked about RAID and Bricks:</font></div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><font face="Input Mono"><i><br>
</i></font></div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><font face="Input Mono"><i>"A typical Gluster configuration
would use RAID underneath the bricks. RAID 6 is most
typical as it gives you 2 disk failure protection,
but RAID 5 could be used too. Once you have the
RAIDed bricks, you'd then apply the desired
replication on top of that. The most popular way of
doing this would be distributed replicated with 2x
replication. In general you'll get better
performance with larger bricks. 12 drives is often a
sweet spot. Another option would be to create a
separate tier using all SSD’s.” </i></font></div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><br>
</div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><font face="Input Mono"><i>In order to SSD tiering from my
understanding you would need 1 x NVMe drive in each
server, or 4 x SSD hot tier (it needs to be
distributed, replicated for the hot tier if not
using NVME). So with you only having 1 SSD drive in
each server, I’d suggest maybe looking into the NVME
option. </i></font></div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><font face="Input Mono"><i><br>
</i></font></div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><font face="Input Mono"><i>Since your using only 3-servers,
what I’d probably suggest is to do (2 Replicas +
Arbiter Node), this setup actually doesn’t require
the 3rd server to have big drives at all as it only
stores meta-data about the files and not actually a
full copy. </i></font></div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><font face="Input Mono"><i><br>
</i></font></div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><font face="Input Mono"><i>Please see the attached document
that was given to me by Red Hat to get more
information on this. Hope this information helps
you.</i></font></div>
<div id="m_523492013473682272bloop_customfont" style="margin:0px"><font face="Input Mono"><i><br>
</i></font></div>
<br>
<div id="m_523492013473682272bloop_sign_1502087376725469184" class="m_523492013473682272bloop_sign"><span>--</span><br>
<div class="m_523492013473682272gmail_signature">
<div dir="ltr">
<div><br>
</div>
<div>Devin Acosta, RHCA, RHVCA</div>
<div>Red Hat Certified Architect</div>
</div>
</div>
</div>
<br>
<p class="m_523492013473682272airmail_on">On August 6, 2017 at 7:29:29 PM,
Moacir Ferreira (<a href="mailto:moacirferreira@hotmail.com" target="_blank">moacirferreira@hotmail.com</a>)
wrote:</p>
<blockquote type="cite" class="m_523492013473682272clean_bq"><span>
<div dir="ltr">
<div>
<div id="m_523492013473682272divtagdefaultwrapper" style="font-size:12pt;color:#000000;font-family:Calibri,Helvetica,sans-serif" dir="ltr">
<p><span>I am willing to assemble a oVirt "pod",
made of 3 servers, each with 2 CPU sockets
of 12 cores, 256GB RAM, 7 HDD 10K, 1 SSD.
The idea is to use GlusterFS to provide HA
for the VMs. The 3 servers have a dual 40Gb
NIC and a dual 10Gb NIC. So my intention is
to create a loop like a server triangle
using the 40Gb NICs for virtualization files
(VMs .qcow2) access and to move VMs around
the pod (east /west traffic) while using the
10Gb interfaces for giving services to the
outside world (north/south traffic).</span></p>
<p><br>
</p>
<p>This said, my first question is: How should I
deploy GlusterFS in such oVirt scenario? My
questions are:</p>
<p><br>
</p>
<p>1 - Should I create 3 RAID (i.e.: RAID 5),
one on each oVirt node, and then create a
GlusterFS using them?</p>
<p>2 - Instead, should I create a JBOD array
made of all server's disks?</p>
<p>3 - What is the best Gluster configuration to
provide for HA while not consuming too much
disk space?<br>
</p>
<p>4 - Does a oVirt hypervisor pod like I am
planning to build, and the virtualization
environment, benefits from tiering when using
a SSD disk? And yes, will Gluster do it by
default or I have to configure it to do so?</p>
<p><br>
</p>
<p>At the bottom line, what is the good practice
for using GlusterFS in small pods for
enterprises?<br>
</p>
<p><br>
</p>
<p>You opinion/feedback will be really
appreciated!</p>
<p>Moacir<br>
</p>
</div>
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