On 01/01/2018 10:10 AM, Yaniv Kaul wrote:

On Mon, Jan 1, 2018 at 12:50 AM, Andrei V <andreil1@starlett.lv> wrote:

Hi !

I'm installing 2-node failover cluster (2 x Xeon servers with local RAID
5 / ext4 for oVirt storage domains).
Now I have a dilemma - use either GlusterFS replica 2 or stick with NFS?

Replica 2 is not good enough, as it can leave you with split brain. It's been discussed in the mailing list several times.

How do you plan to achieve HA with NFS? With drbd?

Hi, Yaniv,
Thanks a lot for detailed explanation!

I know Replica 2 is not optimal solution.
Right now I have only 2 servers with internal RAIDs for nodes, and till end of this week system had to be running in whatever condition.
May be its better to use local storage domain on each node, set export domain on backup node, and backup VMs to 2nd backup node in timed interval?
Its not highly-available yet workable solution.

4.2 Engine is running on separate hardware.

Is the Engine also highly available?

Its KVM appliance, could be launched on 2 SuSE servers.

Each node have its own storage domain (on internal RAID).

So some sort of replica 1 with geo-replication between them?

Could it be the following?
1) Local storage domain on each node
2) GlusterFS geo-replication or over these directories? Not sure this will work.

All VMs must be highly available.

Without shared storage, it may be tricky.

Seems to be timely VM backup to 2nd node is enough for this time.
With current hardware anything above is too cumbersome to setup.

One of the VMs is an accounting/stock control system with FireBird SQL
server on CentOS is speed-critical.

But is IO the bottleneck? Are you using SSDs / NVMe drives? 

I'm not familiar enough with FireBird SQL server - does it have an application layer replication you might opt to use?

In such case, you could pass-through a NVM disk and have the application layer perform the replication between the nodes.

 

No load balancing between nodes necessary. 2nd is just for backup if 1st
for whatever reason goes up in smoke. All VM disks must be replicated to
backup node in near real-time or in worst case each 1 - 2 hour.
GlusterFS solves this issue yet at high performance penalty.

The problem with a passive backup is that you never know it'll really work when needed. This is why active-active is many time preferred.

It's also more cost effective usually - instead of some HW lying around.

 

>From what I read here
http://lists.ovirt.org/pipermail/users/2017-July/083144.html
GlusterFS performance with oVirt is not very good right now because QEMU
uses FUSE instead of libgfapi.

What is optimal way to go on ?

It's hard to answer without additional details.

Y.

 

Thanks in advance.
Andrei

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