Zero System Downtime. How?

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February 9, 2009 at 17:38:13
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Hello. I'm a network engineering student with zero experience (coming from an accounting background). Inspired by the recent flood and power outage problem.I'm doing a paperwork on zero system downtime for business continuity. SAN is out of the question due to it's cost.

My scenario: 3 branch located at different places with one of them hosting the primary server and another one of them hosting the secondary server.

From my theoretical knowledge. I'm suppose to connect these branches with a gateway on each with a permanent public IP. I'm guessing ISDN. So that's my connection. I think that the primary and secondary servers should be sychronised.

Suppose the primary server isn't accesible, how do I make sure the secondary server would take it's place immediately with zero downtime. I heard about failover DNS.

1. What is the best way I could do to connect these 3 branches with security in mind ?
2. What is the best method I can do to synchronize or mirror the primary and secondary server?
3. Everything else I should know

Sorry for my complicated problem and Thank you very much in advance.

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February 9, 2009 at 18:01:16
"...out of the question due to it's cost"

minute you mentioned cost your project was over.

Zero downtime is HUGELY expensive
ISDN would be a bad guess. Expensive and low bandwidth.

You would start with internal site failover.
Servers in a cluster with shared storage is the norm here. Redundant hardware. UpS and failover power. Hourly backups that are replicated off site. Hardware vendors/capital available for replacing all systems.

Then you move on to site to site communication. Dual providers and dual paths to each site. Consider site to site vpns via the internet, Frame Relay, or dedicated Point to Point T1's depending on bandwidth requirements.

That covers the physical. We still have a bunch of OSI layers ahead :-)

Databases? Needs to replicated throughout.
DNS? Needs to be replicated throughout.
Running Active Directory? Site planning throughout.

You may want to spend some time in Google and high availabiltiy servers to start. This will give you a much better idea of server config since there is no such thing as a primary and backup servers. There are hot failover or standby server in a local scenerio but it takes different planning if hosting web sites or you want the secondary site to come up transparently to the users.

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