[OpenAFS] OpenAFS with RAID

Horst Birthelmer horst@riback.net
Wed, 28 Dec 2005 14:29:11 +0100

On Dec 28, 2005, at 1:55 PM, Paul Robins wrote:
>> I just assume you're planning to do this on Linux.
> Yes apologies, linux, probably reasonably modern 2.6 kernel
>> Since there is no other fileserver than a 'namei' on Linux, you  
>> can  use it on any device (the LVM is usually completely  
>> transparent) and  with any filesystem you think it suits best.
> Excellent, that makes things so much easier
>> For the rest of the questions, I don't know how you think you can   
>> 'network' RAIDs.
> I was referring to using something like ENBD to create a RAID array  
> across a network

That's on what I commented further below.
If you put the network somewhere else than in the file system, it's  
getting more complicated.

>> If you want to use available storage from all of your  
>> fileservers,  that's what AFS will help you do.
>> You'll have one namespace and from a users perspective you won't  
>> have  to care about where the storage actually is located.
>> Actually that's what a distributed and even a network file system  
>> is  all about.
> Indeed, what i was referring to is having 4 servers and maintaining  
> some form of redundancy, so that the AFS volume (namespace?) could  
> survive a single server failure, whilst having more than the 180  
> gig currently free on each machine. I kinda assumed it was impossible

So, you expect a network interface failure, or machine failure?
Since you can have a lot of redundancy with your RAID design.

What I meant by 'namespace', is how afs appears on all of your clients.
You'll have a (more or less) fix mount point '/afs' for the AFS  
space. From that point on, everything is 'free'.
You can mount volumes from foreign cells, mount volumes multiple  
times, whatever you want to do.
This tree looks the same on all of your clients.

The replication of volumes in AFS works only for read-only data.  
Maybe you read about that, and that's where most people start getting  
'design ideas'... ;-)

Strictly spoken, you could build that kind of redundancy (something  
like network based RAID 0) with AFS, but I consider that, abusing the  

>> If you think of placing the network some layers lower, like in  
>> the  block device, etc., AFS can't help.
> Yeah i figured as much, i was just wondering if AFS contained any  
> way of doing the above.

Yes and no ...
What you plan is doable with AFS, but I'm not sure you'll get an  
optimal solution by just using AFS.
Maybe you have to reconsider, what data should survive a machine  
failure, etc. and how your disaster recovery would look like.