[OpenAFS] OpenAFS with RAID
Wed, 28 Dec 2005 13:37:32 +0000
I'll reply in one if that's ok (sorry for the topposting)
I would expect a disk to be the thing to go to be honest but regardless,
i want some system where there is parity data stored on other nodes in
this group of machines. Basically RAID5 but networked would be perfect,
as that would give me ~ 400 gig of space whilst being able to handle a
machine vanishing from the network (the whole machine dies when the disk
does, cheap whiteboxes don't you know)
I understand the way AFS works with regards to clients seeing /afs, and
i did see read only replication, and then running a command to change a
read only node(?) into a read write node (i'm sorry if i'm talking crap,
i'd read the wiki if i could). This is why i figured perhaps it could be
implimented with some sort of networked RAID5, giving me a lot more
storage than just RO mirroring one server to the other 3, but whilst
still being redundant.
Thanks for the help,
Horst Birthelmer wrote:
> 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.