[ovirt-users] Good practices

Tue Aug 8 09:09:47 UTC 2017

Fernando,

Let's see what people say... But this is what I understood Red Hat says is the best performance model. This is the main reason to open this discussion because as long as I can see, some of you in the community, do not agree.

But when I think about a "distributed file system", that can make any number of copies you want, it does not make sense using a RAIDed brick, what it makes sense is to use JBOD.

Moacir

________________________________
From: fernando.frediani at upx.com.br <fernando.frediani at upx.com.br> on behalf of FERNANDO FREDIANI <fernando.frediani at upx.com>
Sent: Tuesday, August 8, 2017 3:08 AM
To: Moacir Ferreira
Cc: Colin Coe; users at ovirt.org
Subject: Re: [ovirt-users] Good practices

Moacir, I understand that if you do this type of configuration you will be severely impacted on storage performance, specially for writes. Even if you have a Hardware RAID Controller with Writeback cache you will have a significant performance penalty and may not fully use all the resources you mentioned you have.

Fernando

2017-08-07 10:03 GMT-03:00 Moacir Ferreira <moacirferreira at hotmail.com<mailto:moacirferreira at hotmail.com>>:

Hi Colin,

Take a look on Devin's response. Also, read the doc he shared that gives some hints on how to deploy Gluster.

It is more like that if you want high-performance you should have the bricks created as RAID (5 or 6) by the server's disk controller and them assemble a JBOD GlusterFS. The attached document is Gluster specific and not for oVirt. But at this point I think that having SSD will not be a plus as using the RAID controller Gluster will not be aware of the SSD. Regarding the OS, my idea is to have a RAID 1, made of 2 low cost HDDs, to install it.

So far, based on the information received I should create a single RAID 5 or 6 on each server and then use this disk as a brick to create my Gluster cluster, made of 2 replicas + 1 arbiter. What is new for me is the detail that the arbiter does not need a lot of space as it only keeps meta data.

Thanks for your response!

Moacir

________________________________
From: Colin Coe <colin.coe at gmail.com<mailto:colin.coe at gmail.com>>
Sent: Monday, August 7, 2017 12:41 PM

To: Moacir Ferreira
Cc: users at ovirt.org<mailto:users at ovirt.org>
Subject: Re: [ovirt-users] Good practices

Hi

I just thought that you'd do hardware RAID if you had the controller or JBOD if you didn't.  In hindsight, a server with 40Gbps NICs is pretty likely to have a hardware RAID controller.  I've never done JBOD with hardware RAID.  I think having a single gluster brick on hardware JBOD would be riskier than multiple bricks, each on a single disk, but thats not based on anything other than my prejudices.

I thought gluster tiering was for the most frequently accessed files, in which case all the VMs disks would end up in the hot tier.  However, I have been wrong before...

I just wanted to know where the OS was going as I didn't see it mentioned in the OP.  Normally, I'd have the OS on a RAID1 but in your case thats a lot of wasted disk.

Honestly, I think Yaniv's answer was far better than my own and made the important point about having an arbiter.

Thanks

On Mon, Aug 7, 2017 at 5:56 PM, Moacir Ferreira <moacirferreira at hotmail.com<mailto:moacirferreira at hotmail.com>> wrote:

Hi Colin,

I am in Portugal, so sorry for this late response. It is quite confusing for me, please consider:

1 - What if the RAID is done by the server's disk controller, not by software?

2 - For JBOD I am just using gdeploy to deploy it. However, I am not using the oVirt node GUI to do this.

3 - As the VM .qcow2 files are quite big, tiering would only help if made by an intelligent system that uses SSD for chunks of data not for the entire .qcow2 file. But I guess this is a problem everybody else has. So, Do you know how tiering works in Gluster?

4 - I am putting the OS on the first disk. However, would you do differently?

Moacir

________________________________
From: Colin Coe <colin.coe at gmail.com<mailto:colin.coe at gmail.com>>
Sent: Monday, August 7, 2017 4:48 AM
To: Moacir Ferreira
Cc: users at ovirt.org<mailto:users at ovirt.org>
Subject: Re: [ovirt-users] Good practices

1) RAID5 may be a performance hit-

2) I'd be inclined to do this as JBOD by creating a distributed disperse volume on each server.  Something like

echo gluster volume create dispersevol disperse-data 5 redundancy 2 \
$(for SERVER in a b c; do for BRICK in $(seq 1 5); do echo -e "server${SERVER}:/brick/brick-${SERVER}${BRICK}/brick \c"; done; done)

3) I think the above.

4) Gluster does support tiering, but IIRC you'd need the same number of SSD as spindle drives.  There may be another way to use the SSD as a fast cache.

Where are you putting the OS?

Hope I understood the question...

Thanks

On Sun, Aug 6, 2017 at 10:49 PM, Moacir Ferreira <moacirferreira at hotmail.com<mailto:moacirferreira at hotmail.com>> 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!

Moacir

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