Quick overview of VMware and SAN needed

[nugget]

Hi all. I am looking at getting a second ESX server and would like a quick overview of how the ESX works with vmotion and SANs.

Some questions I have are, is the SAN directly attached to the ESX server(s) (and how) or is connected via ethernet? In relation to this, when using vmotion to "move" a VM from one host to another am I right in thinking the the VMs are stored on the SAN and only the control of the VM is moved to the new host?

Would I need a SAN at all or is it possible to use just local storage space?

The reason is that the second ESX server will be on a different floor.

Any help appreciated.

[zcapr17]

Hi Nugget,

In order to be able to VMotion, you need:

• Shared storage (i.e. a SAN or NAS) where both hosts can see the all the LUNs.
• Compatible CPUs in both hosts.
• GB Ethernet connecting the hosts.
• Virtual Center (with both hosts managed by it).
• Active licenses for VMotion and VC agents.

The shared storage can be a Fibre Channel SAN with the hosts and storage all connected by a Fibre Channel switch, or an iSCSI SAN with the hosts connected by Ethernet (software or hardware initiators can be used). You can also do VMotion with VMs that reside on NFS shares, but it's really really slow (i.e. not for production).

You need to make sure the CPUs in both hosts are compatible, and you need Virtual Center to co-ordinate the VMotion. You will need GB Ethernet between the hosts, and ideally another separate network if you use iSCSI.

I right in thinking the the VMs are stored on the SAN and only the control of the VM is moved to the new host?

Yes

Would I need a SAN at all or is it possible to use just local storage space?

You can't VMotion a VM on local storage, you need a SAN or NAS (i.e. NFS).

HTH.

David

[Luddym]

Absolutely class reply. Rep given.

[nugget]

Thanks for the info David. I've been checking out the vmware site about vmotion but it's still confusing.

Originally Posted by vmware

Migrate any virtual machine running any operating system across any type of hardware and storage supported by VMware ESX, including Fibre Channel SAN, NAS and iSCSI SAN.

If vmotion is limited to using only SAN or NAS for storage then they should indicate that you can only use them and not use any type of storage including them.

Edit: also, the diagrams and wording on the website are also misleading. When I read it I get the idea that I can have 2 vmware servers on the network and move 1 vm on the local storage to the second vmware servers local storage. To me this is moving a vm from one server hardware to another servers hardware as shown in the diagram. Now, if the vm is actually stored on central storage (eg SAN) then you're not moving the vm from one server hardware to another, but just the control files needed for it. A very big difference in my book. Do I make any sense?

[Luddym]

Originally Posted by nugget

Thanks for the info David. I've been checking out the vmware site about vmotion but it's still confusing.



If vmotion is limited to using only SAN or NAS for storage then they should indicate that you can only use them and not use any type of storage including them.

Edit: also, the diagrams and wording on the website are also misleading. When I read it I get the idea that I can have 2 vmware servers on the network and move 1 vm on the local storage to the second vmware servers local storage. To me this is moving a vm from one server hardware to another servers hardware as shown in the diagram. Now, if the vm is actually stored on central storage (eg SAN) then you're not moving the vm from one server hardware to another, but just the control files needed for it. A very big difference in my book. Do I make any sense?

Hi Nugget.

You make perfect sense, however...

Vmotion can only be used with networked storage, SAN, NAS etc. When a VM is transferred to another ESX server using Vmotion, the actual VM's stay on the same networked storage, and it is only the control of it that changes.

From the VM Link

The entire state of a virtual machine is encapsulated by a set of files stored on shared storage, and VMware’s VMFS cluster file system allows both the source and the target VMware ESX server to access these virtual machine files concurrently.

You probably already know that you can manually transfer VM's from one datastore to another using the VI Client, but the actual VM needs to be powered off.

[nugget]

Thanks Luddy. I'm slowly learning the realities of it all but why do they not say this to start with.

Only uses networked storage.
VMs are stored here and not locally to each server.
Only moves the "controlling" files, vm actually stays on the networked storage.

Quite simple (and truthful) to put it this way and more importantly, it's how the bloody thing works. Everything I've read so far points to the opposite.

[Luddym]

I know exactly what you mean.

When we bought our ESX and DR kit (before I got here I might add), we bought blades with lots of raid storage, then locally attached MSA's... and were told that VMotion would work for us.

Now we are stuck using vReplicator, which works pants for us, but that's a whole other story.

[Phoenix]

who on earth told you vmotion would work with locally attached MSAs? Unless they thought it was a locally attached FC MSA to two boxes lol

The gist of it is

The VMDK stays on the Storage, hence the storage needs to be accesible to both servers
on the NAS front only NFS is supported
on the SAN front you have FC and iSCSI options

Storage vMotion came with 3.5 which opens a whole new ball game! but we wont go into that

ESX 1 and ESX 2 must be on the same network
ESX 1 and ESX 2 must have the same, or masked CPUs
ESX 1 and ESX 2 must have the same network labels
ESX 1 and ESX 2 must both be connected to the same shared storage platform

[nugget]

Hi guys, thanks for all the input. I've decided to knock the project on the head for the time being as it's just too much new and unexplored areas in too short a time.

At least now I know what I'll need to look for in the future.

[Luddym]

Originally Posted by Phoenix

who on earth told you vmotion would work with locally attached MSAs? Unless they thought it was a locally attached FC MSA to two boxes lol

Uhm.... we had a consultant who was an 'expert' on pretty much everything. Thankfully it was before my time here.

[Phoenix]

Those consultants give me a bad name