[OpenAFS] Replication, Fail-over, Disconnected Operation and Caching

[Jeffrey Altman]

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openafs@bobich.net wrote:

> I see, so replicated volumes are static, rather than constantly catching 
> up?

Currently, AFS support read-only replication but not read-write replication.

A .readonly volume is paired to a read-write volume.  The "vos release" 
command will copy the current contents of the read-write volume to the 
.readonly volume.  A .readonly volume may have replicas on multiple file 
servers.

>>> 4) If the read-write server fails, how does OpenAFS handle failing 
>>> over to
>>> the replicated backup? When the original master comes back up, how
>>> transparently / gracefully does this happen?
>>>
>>
>> For read-write, you can't see it. For readonly, a volume is a volume.
> 
> So, mounting a read-write volume doesn't transparently fail and promote 
> the backup.

There are two types of mount points in AFS:  Normal and read-write.  A 
normal mount point will always prefer a readonly volume over a 
read-write volume.  A read-write mount point will always use the 
read-write volume.  Once a read-write mount point has been traversed in 
a path, all subsequent mount points will be evaluated as read-write 
mount points.

Clients will failover for .readonly volumes from file server to file 
server.  There is no failover for read-write volumes because there is 
only a single instance of a read-write volume.

Jeffrey Altman

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