[ovirt-users] oVirt & gluster - which copy is written to?

[Sahina Bose]

On 05/12/2016 05:35 AM, Bill Bill wrote:
>
> Hello,
>
> Let’s say I have a 5 node converged cluster of oVirt & glusterFS with 
> a replica count of “3”.
>
> Host1 - replica
>
> Host2 - replica
>
> Host3 - replica
>
> Host4
>
> Host5
>
> If I spin a VM up on Host1 – does the first replica get created local 
> to that server?
>
> In the event I move the VM to another host, does the replica of the 
> disk follow the VM so essentially it’s writing to a local copy first 
> or does it “always” write across the network.
>

Any writes are written to all 3 hosts that form the replica 3 gluster 
volume. Replica 3 - indicates that there is a 3-way copy of data, and 
the same data resides on Host1, Host2 and Host3.

Reads however are from local host. So for a VM running on Host1, it will 
access the data (i.e. read) from the brick on Host1.

> For example, with VMware, the disk will follow the VM to the 
> hypervisor you move it to so that the writes are essentially “local”.
>
> I have not been able to find anything on the internet or in the 
> documentation that specifies how this process works. Ideally, you 
> wouldn’t want a VM residing on Host1 that accesses its disk on Host3. 
> Multiple that by hundreds of VM’s and it would create a ton of 
> unnecessary network congestion.
>
>
>
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