[Gluster-devel] Architecture advice

[Daniel Maher]

Gordan Bobic wrote:

>> How does the HA translator choose a node, exactly ?  Does it randomly 
>> select one from the list of available subvolumes, or does it pick them 
>> in the order they're specified in the config file, or some other way 
>> entirely ?
> 
> Not sure what the default is, but you can specify a preferred read 
> server (writes have to go to all servers regardless) with
> "option read-subvolume" in the volume spec.

option read-subvolume is available only in the AFR translator, and if 
AFR is being done on server-side (the scenario noted previously in this 
thread), then there would be no AFR declaration in the client spec file, 
and thus no way to set the read-subvolume option.

The HA translator is not that useful in the context of a straightforward 
client-side AFR setup in any case, since (as i understand it) if a given 
server dies, the client continues to interact with the remaining defined 
servers seamlessly.  This, of course, is part of the attraction of 
defining AFR on the cleint side ; but in cases where it is not feasible 
(overhead concerns, etc...), using HA with server-side AFR is a very 
interesting prospect.

Some way to extend simplistic load-balancing features to the HA 
translator (or, perhaps, another translator working in concert) would 
therefore be quite ideal.


-- 
Daniel Maher <dma+gluster AT witbe DOT net>