[CentOS] HA with CentOS

Mon May 14 14:44:18 UTC 2007
John R Pierce <pierce at hogranch.com>

Ruslan Sivak wrote:

> If you set up a third box to be the shared storage, doesn't that now 
> become the single point of failure?


enterprise grade shared storage (SAN) is generally fully redundant. They 
use dual storage controllers, ideally in an active/active 
configuration.   you use dual fiber channel cards on each host, going to 
two seperate FC switches, both switches go to both storage controllers.  
each drive bay has fiber loops to both controllers.  fiberchannel drives 
have dual ports so both controllers can talk to them...   Each storage 
chassis has redundant power, ideally wired to seperate UPS systems.      
This is all rather expensive but there is no single point of failure.    
Combined with the fact that every component of this sort of SAN is 
engineered for very high uptime in the first place, you achieve 5 9's or 
better reliability.