Installing ESX server and virtual machines

I have seen scenarios where they install ESX server and later they join it to the SAN. I don't know initially what files get installed in the local server and what get installed as files when they connect it to the SAN.
As of virtual machines when they get created, I am not sure what files get installed locally and what files get installed in the SAN.

I've done SAN architecture for the VMware environment but not much of the software installation.  Perhaps another expert can answer the rest of your question specifically, but anything that you want to be shared between several ESX servers needs to be on the SAN.  It really depends on what you are trying to do.  Are you isolating ESX servers or are you trying to create farms that are able to share workload of the guests?

I have a couple of ESX farms where we are installing ESX on local disk.  The Fiber cables are disconnected from the server during the installation of ESX.  All ESX files are stored locally  Once ESX is installed and patched, connect the cables, zone and mask the storage (or have your storage guys do that) then add the storage in the VMware Infrastructure client and format them as VMFS3 datastores.  VMFS3 is a file system, Virtual Machine File System 3, like NTFS.

It is on these datastores that you will build your virtual machines (guests).  As you add more ESX servers (hosts) to the environment you can zone and mask them to the same LUNs and scan the bus, they'll see the existing datastores and be able to run VMs stored on those LUNs or build VMs in the existing stores.    These groups of ESX servers sharing SAN LUNs are commonly referred to as ESX farms.  If you use Virtual Center you can configure ESX clusters to provide HA (High Availability) and DRS (Dynamic Resource Scheduling).  You will also have Vmotion available, which allows you to move running guest VM from one host to another without interruption of that guest.  DRS leverages Vmotion to prevent over utilization of CPU and Memory resources on any one host in the DRS cluster.  It is not load balancing because it will only make a recommendation to move a guest or actually vmotion a guest when one host has passed a utilization threshold.  So you could have one host with no guests running and the other with 10 and DRS would not do anything as long as the host with 10 has adequate resources.

The only reason to build local vmfs3 datastores is to support Microsoft clustered VMs.  There are other ways to provide HA DR for a VM that are probably better options.  We have not built a Microsoft cluster in ESX to date and will advise against doing so.

Cevans1a:

1-Let's say the storage guys reserved a LUN with huge disk space, and I have formated the LUN with VMFS.
Now Can I add multiple hosts and multiple guests to the same VMFS? if so , is this called a Farm?

2-if Each ESX server Host has its own LUN and its own VMFS where its Virtual Machines are installed. is not this a farm?

3-Can I format one LUN with multiple VMFS and each VMFS will have one ESX server host and Virtual machines that belong to each host? example:
Lun1 will have VMFS1, VMFS2  and VMfS1 will have ESX server1 and VM1,VM2,VM3, VMFS2 will have ESX server2 and VM4,VM5,VM6

LUN2 will have VMFS3,VMFS4 and VMfS3 will have ESX server3 and VM7,VM8,VM9, VMFS4 will have ESX server4 and VM10,VM11,VM12

4-DRS is used only in VMWARE Cluster. correct, how do you make your vmware farm as a cluster? do you meed a software to install on ESX server or on a virtual center?

5-in your comment above you said:

<<<The only reason to build local vmfs3 datastores is to support Microsoft clustered VMs>>>>
Does that mean you cannot have a cluster with vmfs in the SAN?

Thanks