Re: Q: Cluster File System Reliability

On Sep 2, 12:30 am, The Natural Philosopher <a...@xxx> wrote:
nicc777 wrote:
Hi there,

I am rather new to cluster file systems, so let me state my
requirements, and hopefully the kind people here get point me in the
right direction.

Basically I want a file system spanning multiple physical hosts, but
mounted on a server as a single mount point - almost like having some
kind of RAID over various physical nodes. The idea is that if one node
fails, the server should still be able to continue with processing
(assume it's something like a database). I am hoping that when the
failed file server(s) come back online, the "RAID" should be rebuild
on the fly, like a real RAID. This will be first prize.

Not much to ask...is it? :-)

If the above is not possible, or if the performance penalty is too
high, I will also settle for a real time mirroring solution, but with
one crucial requirement: the write on the remote file server (the
mirror) should be guaranteed - in other words, first ensure the data
is on the remote host before writing to the local host disc, and then
only return to the system. I know this will also have a very negative
impact on performance, but I am between a rock and a hard place with
all the requirements (fast file system, but never ever loose any
data).

I think proprietary systems exist, but not on Linux as such. You would
need to hack some code I think.

I can concieve of one Linux box running a custom daemon talking to
similar and intercepting network file requests and sharing them out
amongst the other machines..use synchronous writes to ensure data
integrity, and loads of RAM to cache files with..



You might use linux as a starting point, but you would be writing your
own code to run on it, I suspect.

Perhaps my requirements can not be met, but then I at least need some
pointer as to the next best thing.

Any help will be greatly appreciated. I will feedback to the group in
months to come as to what eventually worked for us (or didn't work and
why).

Thanks in advance.

PS: if anybody knows something about battery backups for hard drives,
and how to protect the hard drive cache in case of power failures etc,
I would also like to hear some of your thoughts/learnings/experiences.

The solution there is to have UPS and power monitoring to flush caches
and halt further access before the system is taken down.

Rather than asking for a particular solution, how about describing te
exact problem you are trying to solve..like how much storage, and how
much throughput, and what level of integrity.

There may be other approaches that would work..

Ok - here goes...

I am trying to put together an architecture that can handle large
amount of data processing near real time (data of around 10TB per
day), but the processing of data should not be broken by any hardware
failures. Think of an accounting/billing system like you get in mobile
operators (or the telecoms industry in general) - if they have a
critical hardware failure in the billing modules one of two things
could happen: 1) you can make calls for free for a period of time; or
2) you can make no calls at all (system stops you). The two scenarios
depend on how the system is designed to handle situations where the
billing module stops working.

*** I am trying to prevent the billing system from breaking in the
first place. ***

That means a "cluster" with nodes in various physical locations,
working as a single image. I don't know if there is a term for this,
but the best I can come up with is a entire system looking/working
like a RAID5 disk system (maybe the term "grid" also kind of describes
it). Storage obviously makes a big part of the solution, as all the
data that is streamed to the system should be written to disk first to
guarantee that the nodes processing the data can retrieve the data
again (in case of a failure somewhere else in the processing system).
This "raw" data might also be archived from time to time when you are
collecting data for troubleshooting parts of your system - the
captured data can be "re-run" in a simulation environment where you
can recreate a days worth of processing, but perhaps slowed down or
something while you debug (if that makes sense to anybody).

From the commercial products, I think Oracle is the closest in terms
of what I want (11g) - but it would be great if we can put a complete
"open source" solution together that many others can use. Not that I
have something against Oracle per say, but I have this thing against
vendor lock-in, and Oracle is rather good with that.

And yes - I do belief a lot of coding will have to take place.
Personally I am leaning toward something like MPI for the data
processing bits - but still, reliable storage is a problem for me. I
don't know how I can get a distributed (physically) filesystem that
looks and behaves like a single system image (or partition) that would
make for highly reliable data storage.

I hope that sheds some more light of what I want to achieve.

Thanks

Nico

.

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