Thanks Johan, you brought "light" into my darkness! I went looking for the 
GlusterFS tiering how-to and it looks like quite simple to attach a SSD as hot 
tier. For those willing to read about it, go here:

Now, I still have a question: VMs are made of very large .qcow2 files. My 
understanding is that files in Gluster are kept all together in a single brick. 
If so, I will not benefit from tiering as a single SSD will not be big enough 
to fit all my large VM .qcow2 files. This would not be true if Gluster can 
store "blocks" of data that compose a large file spread on several bricks. But 
if I am not wrong, this is one of key differences in between GlusterFS and 
Ceph. Can you comment?


From: Johan Bernhardsson <>
Sent: Tuesday, August 8, 2017 7:03 AM
To: Moacir Ferreira; Devin Acosta;
Subject: Re: [ovirt-users] Good practices

You attach the ssd as a hot tier with a gluster command. I don't think that 
gdeploy or ovirt gui can do it.

The gluster docs and redhat docs explains tiering quite good.


On August 8, 2017 07:06:42 Moacir Ferreira <> wrote:

Hi Devin,

Please consider that for the OS I have a RAID 1. Now, lets say I use RAID 5 to 
assemble a single disk on each server. In this case, the SSD will not make any 
difference, right? I guess that to be possible to use it, the SSD should not be 
part of the RAID 5. In this case I could create a logical volume made of the 
RAIDed brick and then extend it using the SSD. I.e.: Using gdeploy:






devices=sdb, sdc













But will Gluster be able to auto-detect and use this SSD brick for tiering? Do 
I have to do some other configurations? Also, as the VM files (.qcow2) are 
quite big will I benefit from tiering? This is wrong and my approach should be 



From: Devin Acosta <>
Sent: Monday, August 7, 2017 7:46 AM
To: Moacir Ferreira;
Subject: Re: [ovirt-users] Good practices


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.

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.

Here is the direct quote from Red Hat when I asked about RAID and Bricks:

"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.”

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.

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.

Please see the attached document that was given to me by Red Hat to get more 
information on this. Hope this information helps you.


Devin Acosta, RHCA, RHVCA
Red Hat Certified Architect

On August 6, 2017 at 7:29:29 PM, Moacir Ferreira 
(<>) wrote:

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).

This said, my first question is: How should I deploy GlusterFS in such oVirt 
scenario? My questions are:

1 - Should I create 3 RAID (i.e.: RAID 5), one on each oVirt node, and then 
create a GlusterFS using them?

2 - Instead, should I create a JBOD array made of all server's disks?

3 - What is the best Gluster configuration to provide for HA while not 
consuming too much disk space?

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?

At the bottom line, what is the good practice for using GlusterFS in small pods 
for enterprises?

You opinion/feedback will be really appreciated!


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