[Linux-cluster] Cluster Planning
Rainer Duffner
rainer at ultra-secure.de
Thu Apr 20 15:45:13 UTC 2006
Scott Kellogg wrote:
>
>>
>> Also to use an active-active (same service active on both servers)
>> configuration + loadbalancing you will need more than 2 servers; at
>> least 4 servers, 2 for loadbalancing (1 active/1 backup) and 2 for
>> the critical service active concurently on both servers (no high
>> availability, no failover).
>
> You seem to be referring to LVS. Right, I can't implement that since
> I don't have enough hardware. I think that active-passive will be the
> way to go. When the active node dies, the passive node will take
> over. The data will only be as fresh as the last synchronization.
>
> That begs the question of what happens when the active node comes back
> up ... will the passive node (now active) sync its data to the new
> active node? This is where picking a synchronization method becomes
> vital.
That's where GFS comes in.
I don't want to sound rude, but either you (or your customer) have the
budget for a cluster or not.
If you don't have the budget, it's better to just use the 2nd server as
hot-spare and rsync the data over to the 2nd one and do the failover by
hand (and even more so the re-activation of the primary server)
Or you should have bought a more expensive, more reliable server instead
of two low-end ones.
You *can* have low-end servers, but you need a reliable
storage-infrastructure (which will be a SAN in 7 out of 10 cases and
iSCSI in the other), which has a big upfront-cost.
This always reminds me of people who want to drive cars they cannot
really afford.
It's better to acknowledge that and accommodate to a cheaper car than
sitting there one day without the money to have it repaired....
cheers,
Rainer
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