[Gluster-users] keep qcow2 images in sync

[Guy Boisvert]

On 2019-06-29 7:26 a.m., Marcus Schopen wrote:
> Hi,
>
> i am looking for a solution to keep qcow2 images of two KVM hosts sync.
> (about 20 guests, images size max 100 GB). Unfortunately, shared
> storage is not available to me. My first look was on Gluster, but after
> what I've read so far, there might be performance issues here. I don't
> need real HA. If the first host fails, it would be sufficient for me to
> manually start the KVM guests on the second host. Ultimately, I just
> want to avoid having to restore the images from the nightly backup and
> have a maximum "data loss" of 24 hours. Is drdb a alternative here? And
> what should I pay particular attention to when setting up, split brain
> etc.?
>
> Cheers
> Marcus


Hi Marcus,

     I use GlusterFS for VM image storage.  Most of them are RAW files 
and QCOW2 is fine too.  There are things to watch for performance.  In a 
setup we have for a client, the Windows File server (8TB + 5TB) is now 
screaming compared to the old setup: 120 MBps!  And the overtaxed mail 
server (CentOS 7 Linux VM running CommuniGate) on the same cluster is 
doing fine too (low IOwait considering the 1TB+ Public Folders, 140 
Outlook users and a total of 2.5 TB of emails).

     This setup is configured in three way replication.  The 3 servers 
are Supermicro using LSI RAID 6 arrays.  GlusterFS bricks are ontop thin 
provisioned LVM logical volumes.  Watch out for lvm / filesystem optimal 
alignment VS your physical RAID arrays.

     Just keep in mind that with 2 servers, you are exposed to split 
brain issues.  The other way of doing it in the above setup would be 2+1 
replication with an arbiter: It would saves space and still enforce 
quorum.  But many things i read are pointing to 3 way replication for 
simplicity and stability.


Here are the infos about this Gluster cluster:

3 x Supermicro 3U servers with each:

1 x Xeon E5-2609 CPU

32 Gig RAM

Integrated LSI SAS 2208

32 TB Array consisting of 8 x HGST NAS 7200 RPMs drives in RAID 6

2 x Integrated Intel X540-AT2 10 Gbps ethernet

We are considering of adding SSD caching, still looking for the best way 
of doing it... (LVM Cache  / Gluster Tiering / etc)


There are 2 KVM Servers running VMs with dual E5-2630v2 CPU, 96 Gigs RAM 
and dual 10 Gbps ether

The next part will be to add OVirt.


Be sure to simulate what you want to achieve before going in prod.  Test 
disconnection of a node, etc.  I like Gluster but there are situations 
that you must know what you're doing.  I paid a premium for the Red Hat 
Gluster Video self training and it is not a good course IMHO (more of an 
intro...), i didn't learn what was of interest to me (highly technical) 
and i taught i could ask questions: They direct you to tech support and 
you must have a contract.... They seem to want to direct you to their 
"design" team.

I didn't find any "best practices", not real good guidelines and 
explanations...

A real important thing to consider: The network part.  Look for bonding 
+ dual attach switch and for ECM Routing + OSPF on the servers / 
network.  I'm still searching for the best network setup to get 
performance and full redundancy.


Hope this helps.


Guy

-- 
Guy Boisvert, ing.
IngTegration inc.
http://www.ingtegration.com
https://www.linkedin.com/pub/guy-boisvert/7/48/899/fr

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