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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