[OpenAFS] Getting started with OpenAFS

Todd Lewis utoddl@email.unc.edu
Fri, 30 Apr 2010 08:32:34 -0400

On 04/30/2010 07:07 AM, Mike Pliskin wrote:
> - speed is important as well as a way to access any file from anywhere (but ok to degrade speed if replicas aren't synced yet)

Your "replicas aren't synced yet" phrase indicates you're still under 
the assumption that so many people start with -- that the ro replicas 
are somehow automatically synced in near real time from the single rw 
volume. They are not. It's a manual process, or scripted, which pushes 
the volume image from the rw server to the ro replicas.

Think of it more as a publishing operation. Everybody else is reading 
"today's edition" of some ro volume, while a few people are preparing 
the next edition. It could involve lots of changes across the volume 
that don't make sense separately, but only as a complete set of changes. 
Once you've got the contents of the rw volume consistent and the changes 
are complete, then you "release" that volume. The ro replicas get the 
changes in one go. If your users are geographically distributed, then 
the hope is that the ro volume they are using is on a server that is 
relatively close to them so the data has only to cross slow/long network 
links once -- during the release operation -- rather than as they read data.

Writes/updates still have to get to the single rw volume across whatever 
network hops it takes.

Note also that the path to a rw volume will differ from the path to its 
ro replicas (unless you've configure the client to use only rw volumes 
throughout your cell).