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Re: [Linux-cluster] Re: E-Mail Cluster



Nicholas Anderson wrote:
Hi again all .....

I guess i'm starting to understand how the things should work ....

I was reading about GFS and all the documents that i found suppose that you have a storage with a SAN and 2 or more machines connected through FC to the SAN. Well, it seems to me that in this case the storage or the SAN switch still being one single-point-of-failure right? If the storage or SAN goes down, the whole service will be offline right ?

First of all, you (should) have redundant FC-switches (mulipathing).
Then, your storage has (should have) multiple controllers. Eg. HP EVA series. If that isn't enough, there are solution to mirror the storage at the hardware-level. Usually, this is in the "if-you-have-to-ask-it's-probably-too-expensive-for-you-anyway"-pricerange and thus only used where the (lack of) downtime is worth the investment.



I thought that with GFS i could do something like a "Parallel FS" where 2 (or more) machines would have the same data in their disks, but this data would be synchronized in realtime .... am i totally noob or there really has a way to make FS's work in parallel, synchronizing in realtime? I'd like to do this without having a SAN (cause i don't have one :-) and i have only 1 storage ) and without leaving a single-point-of-failure.

Let me try to explain exactly what I'm thinking ...

3 servers, each one with a 300GB SCSI disk (local, no FC) to be synchronized with the others (through GFS?? mounted and shared as a /data f.ex.), and one 36GB disk only for the SO. All the servers would have smtp(sendmail with spamassassin and clamav), imap and pop3 services running, and probably a squirrelmail.



You can have a master/slave solution with DRBD.


Is it possible to do this? Is it possible to get this data synchronized in realtime ?


I don't think so.
Well, Google has sort-of a solution via their "Google Filesystem". But not for you or me. :-(



Thanks again for your really really important answers, and sorry for asking so much noob questions :-)



IMO, hardware is very reliable these days (if you choose wisely). Things like DRBD seem (to me) only useful in very special cases - and I would fear that DRBD might create more problems than it solves. In your special case (email), if you can't afford a SAN, get a used NetApp and store the maildirs there (qmail-style maildirs). Then NFS-mount them on the "cluster-nodes". The NetApp is reliable enough for these scenarios and depending on the exact model, already contains a lot of redundancy in itself.





cheers,
Rainer


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