How High Availabilty works??

[spikfrank]

If I were to summarize the way HA works, am I correct by saying:

You have one SAN with 2 or more VM Host's connected to it. The VM's are stored on the SAN. If one of the VM Hosts goes down, another VM Host detects it and brings it's virtual machines back up.

[a_p_]

Yes, that's basically it. see http://www.yellow-bricks.com/vmware-high-availability-deepdiv/ for more info on HA

André

[idle-jam]

here is a video of HA in action @ http://www.youtube.com/watch?v=iruACplfHC4

[AndreTheGiant]

HA as some "agent" on each hosts, so can works without vCenter Server (for this reason you can run vCenter in a VM without big issues).

HA can do several things:

• Admission Control: you can ensure to have enough free resources in a case of a failure
  
• Host monitoring: check if hosts are alive (the check is only network based)
  
  • Host failure detection: when a host as a failure
    
  • Host isolation detection: when a host is still working, but has no networking connectivity (at least in the network part used by HA)
    
  • VM restart
    
• VM monitoring: check if VM are responing (this is done with VMware Tools pulse)
  
  • VM restart
    
• VM service monitoring (from vSphere 4.1): require special API in the applications
  

Note that there is no storage failure detection, HA works with networking-based tests (for hosts detection).

See also Duncan Epping articles and/or the "HA and DRS Deepdive" book (http://frankdenneman.nl/2010/08/vsphere-4-1-ha-and-drs-deepdive-book/)

PS: thread moved to the proper forum area.

Andre