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@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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