Re: [SLUG] Network Real-Time Hot Filesystem Replication?

[Jamie Wilkinson <jaq@xxxxxxxxxxxxxx>]

This one time, at band camp, Crossfire wrote:
> Dave Kempe wrote:
>> Crossfire wrote:
>>> I want to be able to set it up so /home (and maybe other filesystems) 
>>> are replicated from one to the other, in both directions, in real 
>>> time so they can run in an all-hot redundant cluster.
>>>
>>> The environment should be mostly read-oriented, so I can live with  
>>> write-latent solutions as long as they handle the race/collision  
>>> gracefully (preferably by actually detecting and reporting it if they 
>>> can't avoid it).
>>>
>> isn't this just a description of a network filesytem... say NFS?
>
> No.  Network Filesystems still have a distinct single storage location.  
> If that storage is taken offline, clients can only error or hang.
>
> With a hot real-time replicated filesystem, all involved nodes would  
> have a full local copy at all times and would be able to continue 
> operation.

I agreed with your earlier decision about not using drbd because you
wouldn't be able to write from multiple nodes to the filesystem; all the
slaves would have to be mounted read-only.  However if you wanted to get
fancy you could still use drbd (which is a great fit for all your other
requirements) on a multi-node fileserver, and do some nifty failover using
IP takeover.

Or if you're trying to share the local disk of a lot of nodes, then what if
you used DRBD on them all to replicate the block device, and run a NFS
server on the nodes thremselves?  Yes you'd get a lot of network traffic
between them, but it'd work, no? :)