[Gluster-users] Read from fastest node only

Tue Aug 3 17:51:48 UTC 2021

md-caching is not a panacea for your case, but it could help to some extend.
The difference between thin and usual arbiter is that the thin arbiter takes in action only when it's needed (one of the data bricks is down) , so the thin arbiter's lattency won't affect you as long as both data bricks are running.
Keep in mind that thin arbiter is less used. For example, I have never deployed a thin arbiter.
Best Regards,Strahil Nikolov

  On Tue, Aug 3, 2021 at 7:40, David Cunningham<dcunningham at voisonics.com> wrote:   Hi Strahil,
I registered and read the article, thank you. It looks like it would help the speed of directory listing and related operations, but I don't see anything to suggest that the other nodes won't be checked on file reads. Am I missing something?
We would probably use something like 2 nodes nearby and 1 remote. I understand that the thin arbiter keeps a track of which nodes are online, but can't see how that will help with file reads and nodes being checked for consistency. Are you able to explain please?
Thanks.

On Mon, 2 Aug 2021 at 17:45, Strahil Nikolov <hunter86_bg at yahoo.com> wrote:

Hi David,
Can you register at developers.redhat.com and check the article about the md-cache. I think that for most cases the caching should be sufficient in order to not lookup the remote node.
By the way, are at least 2 of nodes nearby (lower lattency)? If only 1 node is 'remote' , then you can give a try to gluster's thin arbiter (for the 'remote' node).

Best Regards,Strahil Nikolov 

  On Mon, Aug 2, 2021 at 5:02, David Cunningham<dcunningham at voisonics.com> wrote:   Hi Ravi and Strahil,
Thanks again for your responses. Having one brick be the one to read (but with failover if that node goes completely offline) would be great if we could do it per client, but won't work if all clients have to use the same setting.
I'm not sure about gNFS, but normal NFS is something we've thought about as an option. I'm not sure if it will help though, because if the client NFS mounts the server which has the brick, then when it does a read presumably the brick will be checked for consistency with the other bricks and latency will be a problem again. If my understanding is correct even with choose-local enabled the other bricks will still be checked so the problem is not solved.
I confess that AFR vs eventual consistency is beyond my understanding of replication. In the world of SQL there is Galera cluster, and it will write to all nodes but for reads only checks the node the client is actually connected to. That's the sort of functionality we'd find really helpful for our use-case.

On Fri, 30 Jul 2021 at 19:21, Strahil Nikolov <hunter86_bg at yahoo.com> wrote:

Hi David,
md-cache will just save some lookup actions across the bricks, but it won't save you from all cases.
Using gNFS + cluster.choose-local is worth exploring, but as gNFS is deprecated I never checked if it will be affected by the lattency of the last brick.
What Ravi proposed looks promising, but it has some drawbacks - for example a brick dies and FUSE clienta have to be adjusted to read from another brick.
Ravi, I think that this topic was already discussed once.
Best Regards,Strahil Nikolov 

  On Fri, Jul 30, 2021 at 8:49, Ravishankar N<ranaraya at redhat.com> wrote:   ________

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