Booting VMs from SAN

I am about to purchase servers for a virtualisation project and still have one area of uncertainty.
The vmdk files will be stored on the iSCSI server along with the data. I was originally thinking of having the ESXi servers with no disks and the hypervisor installed on an SD card. I was told by a supplier yesterday that the most usual approach is to still have the vmdk files on the SAN but to have 2 disks in RAID1 on each server and to have the hypervisor installed on this array. The reason being that it moves the processing from the SAN server to the ESXi server.

Please can tell me if this is correct and explain why?
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jakethecatukConnect With a Mentor Commented:
Running ESXi on hard disks will not have any bearing on the network traffic from the iSCSI SAN.

Not having a dedicated network for the iSCSI SAN will have an impact on performance.
ESXi can be installed on a USB stick or local disk - it's not supported on an SD card.

I really don't get what your supplier is saying - it sounds like he either doesn't understand ESXi or he's trying to flog you kit you don't really need.
Well considering that ESX does still use swap space and SD Cards/USD sticks only have a limited amount of writes to them it might be a ticking timebomb... (please note i did write might)

The main question you need to ask is if the usb stick dies how important is it, and how soon do you need it up. Reinstalling ESX isn't very hard or time consuming...

With RAID 1 - life is easy one disk dies you just replace it and no down time (providing you have some form of hardware monitoring... :) )
As for the storage the easiest would be to by a NAS (Number of disks depending on the number of hosts you want to put on it).

From my perspective ISCSI just over complicates stuff... and needs more bandwidth
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tangerine27Author Commented:
Just to be certain you understand what I am doing:

2x ESX/ESXi servers
1x iSCSI server

The ESX/ESXi servers would only have SD card/USB stick with the hypervisor.
The iSCSI server would have a RAID10 array for the user data and SQL databases, and a RAID1 array for the vmdk files.

The supplier, whilst saying that was OK, recommended that:
The ESX/ESXi servers would have RAID1 array with the hypervisor installed on it (only).
The iSCSI server would have just a RAID10 array for the user data, SQL databases and the vmdk files.
If you are using ESXi on a USB stick, why would you have a RAID 1 array for the VMDK files on top of the RAID 10 array?

When you configure a virtual machine, you can store all the required data files (config, nvram, swap, vmdk's) in the same location on the iSCSI disks with no problems.  In fact, if you're having two ESXi servers - you should do that anyway to allow for moving VM's between hosts.

Seems like your supplier is suggesting that if you have two internal HDD's then you can store some config information for your VM's on those disks as well...not a good idea IMHO.

JTC - vSphere Certified Professional
tangerine27Author Commented:
Thanks Jake
Are you saying that having ESXi on a USB stick with no hard drives is as good performance wise (processing and network utilisation) as having ESXi on a RAID1 array? (Both these would have the vmdk files entirely and only on the iSCSI server)
royco2Connect With a Mentor Commented:
Your configuration will work. but in event of a failure will require manual labor

What the supplier is trying to do is a standard config and is more like something Vmware would recommend.

I do agree that separating the SQL and vmdk files is a generally good idea.
Flash memory is faster than disk - but as ESXi has a very small footprint, there's not going to be much in it.  Using either will give you a fast stable system.  

If you go the USB route - keep a second USB key pre-built with your ESXi installation just in case your main key fails.  Spend money on a decent USB sticks for the installation (it doesn't need to be huge though - 4gb is more than enough).

If you go down the disk route, make sure your RAID controller is supported by VMWare.

Actually, you haven't said what server you are buying and again, you should make sure it's supported by VMWare -
tangerine27Author Commented:
I understand the points that both of you have made above, but does running ESXi on a hard disk mean that there is less network traffic from the iSCSI server related to the vmdk files, or any other performance benefit?
tangerine27Author Commented:
OK thanks very much to you both for your time.
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