Question : Problem: Experts: Clustered Server Complex Design

http://www.adaptec.com/worldwide/product/markeditorial.html?sess=no&language=English+US&cat=%2fTechnology%2fExternal+Storage&prodkey=raid_family_tool

1)I would like to have a "clustered server" , how the server connected to the External RAID storage?
2)What is HBA? DO we need fibreChannel ?

3)Do we need to have 2 RAID controller on the External Storage?

4)Do we need to have a RAID controller for each of the server?

5)How having 3 servers for this clustered setup, instead having 2 server ?

6)If would like to get a Dell solution, which server and RAID recommended? Any extra RAID card/fibrechannel we need?

7)How the server OS will boot from the External Storage, we need to have a boot loader to boot each of the server?

8)Can we partition the external storeage to 3 partition, and each of the server boot from their own partition.?

-Thx
qazakax .at. yahoo.com

Cheers..We are using LINUX OS.

Answer : Problem: Experts: Clustered Server Complex Design

>This is what i get from one of my "friend's friend":

Hah! Let me put it this way - compared to your plan before you heard what this guy said, how much better off are you now? What is said is useless.
He doesn't tell you what to do and how to do it. He just describes a generic technology for shared disk failover - which is what we've been discussing all this time - where only one server is active on the shared disk at a time and the other one is in stand-by mode, ready to take over.
That's technology that all these scenarios with servers connected to external RAID disk array or FC disk array use.

I suggest you make a list of things you've figured out and the list you haven't and move forward by solving problems and questions that are still unanswered.

For example, if we assume:
a) you've chose external RAID disk array and two servers
b) on the app servers connected to SCSI disk array, you will run Web server and mySQL DB
c) you won't use boot from external SCSI because it's probably not supported and the low SCSI performance (considering that both OS and data would all go thru one SCSI channel - that would cause the data to crawl plus you still need to think about the swap file)
d) for all practical purposes you cannot load-balance mySQL (you can provide it with failover only), you can only load-balance Apache Web servers.
Therefore, your mySQL DB will be on external disk array and your Web content on each server's /var/www/html (or such).

The remaining questions you need to answer for yourself:
a) do you want to have an obvious single point of failure (the load-balancing server) for balancing only two Web servers (Considering the fact that at all times one of them also runs mySQL database, you will probably want to send 75% requests to the non-DB host and 25% to the Web server that's also running mySQL. Since your load-balancing server won't know what mySQL is doing, its balancing won't benefit Apache much. Round robin DNS for which you do not need the third server but just a simple DNS setting is much better a choice)
b) do you want to pay for setup & config of the cluster (which is very imporant because you won't be able to do it yourself; also don't ask that friend's friend to help you)