[Gluster-users] Trying XenServer again with Gluster

Wed Mar 30 01:22:25 UTC 2016

With some recent posts regarding Arbiter, I’m a little confused…

I understand Replica 2 you can’t get a quorum to prevent split brains, but does that only apply to having 2 servers?

If I have 4 servers running distribute 2 replica 2, I still get quorum right?   I don’t need to add an arbiter volume, or do I ?

What if I have 4 servers running distribute 2 replica 2 and I have 2 additional servers that are part of the pool, but not running bricks, do I still need replica 3 arbiter 1 for HA?

> On Mar 22, 2016, at 8:48 AM, André Bauer <abauer at magix.net> wrote:
> 
> Hi Russel,
> 
> i'm a KVM user but imho XEN also supports accessing vm images through
> libgfapi so you don't need to mount via NFS or fuse client.
> 
> Infos:
> http://www.gluster.org/community/documentation/index.php/Libgfapi_with_qemu_libvirt <http://www.gluster.org/community/documentation/index.php/Libgfapi_with_qemu_libvirt>
> 
> Second point is that you need to have at least 3 replicas to get a
> working HA setup, because server quorum does not work for 2 replicas.
> 
> Infos:
> https://www.gluster.org/pipermail/gluster-users/2015-November/024189.html <https://www.gluster.org/pipermail/gluster-users/2015-November/024189.html>
> 
> Regards
> André
> 
> 
> Am 20.03.2016 um 19:41 schrieb Russell Purinton:
>> Hi all, Once again I’m trying to get XenServer working reliably with
>> GlusterFS storage for the VHDs. I’m mainly interested in the ability to
>> have a pair of storage servers, where if one goes down, the VMs can keep
>> running uninterrupted on the other server. So, we’ll be using the
>> replicate translator to make sure all the data resides on both servers.
>> 
>> So initially, I tried using the Gluster NFS server. XenServer supports
>> NFS out of the box, so this seemed like a good way to go without having
>> to hack XenServer much. I found some major performance issues with this
>> however.
>> 
>> I’m using a server with 12 SAS drives on a single RAID card, with dual
>> 10GbE NICs. Without Gluster, using the normal Kernel NFS server, I can
>> read and write to this server at over 400MB/sec. VMS run well. However
>> when I switch to Gluster for the NFS server, my write performance drops
>> to 20MB/sec. Read performance remains high. I found out this is due to
>> XenServer’s use of O_DIRECT for VHD access. It helped a lot when the
>> server had DDR cache on the RAID card, but for servers without that the
>> performance was unusable.
>> 
>> So I installed the gluster-client in XenServer itself, and mounted the
>> volume in dom0. I then created a SR of type “file”. Success, sort of! I
>> can do just about everything on that SR, VMs run nicely, and performance
>> is acceptable at 270MB/sec, BUT…. I have a problem when I transfer an
>> existing VM to it. The transfer gets only so far along then data stops
>> moving. XenServer still says it’s copying, but no data is being sent. I
>> have to force restart the XenHost to clear the issue (and the VM isn’t
>> moved). Other file access to the FUSE mount still works, and other VMs
>> are unaffected.
>> 
>> I think the problem may possibly involve file locks or perhaps a
>> performance translator. I’ve tried disabling as many performance
>> translators as I can, but no luck.
>> 
>> I didn’t find anything interesting in the logs, and no crash dumps. I
>> tried to do a volume statedump to see the list of locks, but it seemed
>> to only output some cpu stats in /tmp.
>> 
>> Is there a generally accepted list of volume options to use with Gluster
>> for volumes meant to store VHDs? Has anyone else had a similar
>> experience with VHD access locking up?
>> 
>> Russell
>> 
>> 
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> 
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> André Bauer
> 
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