[ovirt-users] [GlusterFS] Regarding gluster backup-volfile-servers option

[knarra]

On 05/18/2017 10:35 AM, TranceWorldLogic . wrote:
> Thanks,
> Would you also explain about my 2nd question ?
>
> let say hostB mounted glusterFS partition by using backup vol (e.g. 
> hostB) and after some time Host A come online, will GlusterFS client 
> (mount) automatically switch to Host A ?
mount will not switch automatically to Host A .

In an ideal case i.e with out using backup-vol-file-server option if 
host B goes down, you mount will not be accessible since host B went 
down and df -TH or mount does not show the volume or it says "Transport 
End point not connected".

Take the case where using backup-volfile-server option. If host B goes 
down, your mount will still be accessible since there is 
backup-volfile-server and df -TH or mount still shows that volume is 
mounted using Host B, but all the internal requests will be served 
through Host A.

>
> On Thu, May 18, 2017 at 9:43 AM, knarra <knarra at redhat.com 
> <mailto:knarra at redhat.com>> wrote:
>
>     Hi,
>
>         backup-volfile-servers is mainly used to avoid SPOF. For
>     example take a scenario where you have Host A and Host B and when
>     you try to mount a glusterfs volume using Host A with
>     backup-volfile-servers specified, if Host A is not accessible,
>     mount will happen with Host B which is specified in
>     backup-volfile-server. backup-volfile-servers are mainly used to
>     fetch the volfile from gluster and  has nothing to do with data sync.
>
>         data syncing comes as part of replicate feature in glusterfs
>     where say for example, you have two Hosts Host A and Host B with
>     replica volume configured, if Host A goes down for sometime, all
>     the writes happens on Host B and when Host A comes up data gets
>     synced to HostA.
>
>     Hope this helps !!!!
>
>     Thanks
>     kasturi
>
>
>     On 05/17/2017 11:31 PM, TranceWorldLogic . wrote:
>>     Hi,
>>
>>     Before trying out, I want to understand how glusterfs will react
>>     for below scenario.
>>     Please help me.
>>
>>     Let consider I have two host hostA and hostB
>>     I have setup replica volume on hostA and hostB. (consider as
>>     storage domain for DATA in ovirt).
>>     I have configure data domain mount command with backup server
>>     option (backup-volfile-server) as hostB (I mean main server as
>>     hostA and backup as hostB)
>>
>>     1> As I understood, VDSM execute mount command on both hostA and
>>     hostB.(for creating data domain)
>>     2> That mean, HostB glusterFS CLIENT will communicate with main
>>     server (hostA).
>>     (Please correct me if I am wrong here.)
>>     3> Let say HostA got down (say shutdown, power off scenario)
>>     4> Due to backup option I will have data domain available on HostB.
>>     (Now glusterFS CLIENT on HostB will start communicating with
>>     HostB GlusterFS SERVER).
>>     5> Now let say HostA comes up.
>>     6> Will it sync all data from HostB to HostA glusterFS server ?
>>     (as per doc, yes, i not tried yet, want to confirm my understanding)
>>     7> Will glusterFS CLIENT on HostB start communicate with main
>>     server (HostA) ?
>>
>>     Please let me know, I am new to glusterFS.
>>
>>     Thanks,
>>     ~Rohit
>>
>>
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