[OpenAFS] Getting started with OpenAFS
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).