NFS failover with shared folder sync/replication?

[ninja888]

Hi There!

I have a couple of Synology NAS currently and I wondered whether there was a way to sync NAS1 shared folder A to NAS2 shared folder A such that, if NAS1 goes down, NFS (and potentially CIFS, etc) connections from clients would automatically failover to NAS2?

I'm aware of Synology High Availability (SHA) which would do this but (A) my two NAS are not compatible together for SHA and (B) I believe SHA requires the entire NAS1 to be replicated to NAS2 rather than select shared folders?

Has anyone done anything similar with say Shared Folder Sync / Snapshot Replication, perhaps with a NFS Load Balancer in front of both NAS?

Thanks!

 

[Rusty]

Snapshot Replication tool can do this. It has a failover solution. BRTFS on both NAS is needed and both NAS need to have S&R package.

 

[ninja888]

Great, thanks Rusty!

just had a look at the Synology Snapshot Replication feature and it can replicate a snapshot between a source NAS1 and destination NAS2 but it seems their definition of failover is more to do with manually changing the direction of the replication from NAS2 to NAS1 rather than doing anything clever with informing the NFS clients of a failover so I’ll likely have to research some form of NFS load balancer in front of both NAS?

Thanks!

 

[fredbert]

How are you sync'ing the files between the two NAS? If a file is being worked on during failover ... what do you expect to happen to the client's copy and edits?

Maintaining connections through failover on network devices is one thing, passing the connection routing between clustered routing/FW/etc devices, but keeping the end data in sync is a level up ... in my experience, which has been at the connection level rather than application data.

At the backend you'll have to have the various NAS maintain their data in sync: Drive ShareSync? Or some such.

At the frontend you'll need some connectivity load balancing to hide that the single (global) connection address is fed by multiple NAS. However, that load balancer will have to be able to re-authenticate the new connection in the event of failover ... do you want your credentials cached? OK so that's probably no. In that case they will probably either lose work when trying to write back (lost connection due to not authenticate on failover NAS ... it gets the packets but has no open, authenticated file sharing connection) or they are perplexed because they are asked to re-authenticate.

What happens when the load balancer fails? You still have a SPOF unless it too supports HA resilience. Then do you have dual links on your network etc etc etc etc until you're fully resilient on LAN and to the Internet.

The alternative is to maintain backend sync to the secondary NAS and notify users of planned downtime on the primary. If they know the different connection addresses then they'll be able to reconnect to the secondary.

I think what you're looking to do is very application specific and adding external load balancing will have to be tested to ensure it does what you need.