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,
Paul
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
design.
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.
Horst
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