Boot vhd has to be IDE on Hyper-V?

[Guest darosant]

Hi,

Thanks for your instructions on how to import a VM into Windows 2008 Hyper-V. I am now creating a new VM from scratch and was surprised to learn that the boot vhd has to be an IDE disk. Is this how it works? I was able to create VM under Windows 2003 R2 with bootable SCSI disks. Is there a workaround for this issue?

 

Thanks in advance for any information.

David

[Steve Krause]

Been awhile since I've played around with this. I'll play around with it tmow and let ya know what I find.

 

Is there any particular reason you want to use a SCSI drive for the .vhd?

[Guest darosant]

My understanding is that with SCSI emulators in VM the performace is much better. The other detail is that with IDE drives the vhd maximum size is 127GB. Nevertheless I'm thinking that the boot drive can be IDE and the data disks which will be much bigger than 127GB can be SCSI. I've been using SCSI drives since Novell 3.11, NT 4 and so on. Feels weird to go back to an IDE drive although it is virtual.

 

David

[alexmvp]

Take a look at this thread. http://blogs.msdn.com/virtual_pc_guy/ar ... 25487.aspx

 

There has been some confusion over when users should use SCSI or IDE virtual hard disk inside of their virtual machines. The first thing to note is that it does not matter what sort of physical hard disk you have in your computer when you are making this decision.

 

There are a number of factors to consider:

 

* Our emulated IDE can only support 4 disks, while our emulated SCSI supports up to 28 disks

* Our emulated IDE can only support up to 128GB disks, while our emulated SCSI can support up to 2TB disks

* Our emulated IDE controller has a higher level of driver support for various operating systems than our emulated SCSI controller

 

The final thing to consider is performance - and this is a bit tricky. Contrary to common sense, the performance of our emulated SCSI controller is slower than that of our emulated IDE controller. The reason for this is that the SCSI controller is a lot more complicated to emulate than the IDE controller. Now - this changes once you have Virtual Machine Additions installed. As part of Virtual Machine Additions we install an accelerated SCSI driver. Once this driver is installed the performance of our emulated SCSI controller is significantly faster than our emulated IDE controller.

It actually says the IDE is faster than SCSI however... this is from 2006 so it's quite old.

 

Here's another thread talking about Hyper-V. - http://www.haiders.net/post/Hyper-V-Review.aspx

 

Here's a few quotes I found interesting:

1 - The IDE channels can support upto 2TB of virtual storage.

2 - You can't have a SCSI boot drive! A Hyper-V guest machine can only boot from an IDE drive. While the performance of the new synthetic IDE driver is supposed to be better, if the underlying inteface is SCSI, there has to be some overhead. Most servers are likely to have a SCSI interface. The reason why Hyper-V guest machines can't boot from SCSI has something to do with the new synthetic SCSI driver. Because it does not emulate a real and known SCSI hardware, it seems it can't be booted from! I think it's a lame excuse and a Hyper-V final release better be able to boot from SCSI.

3 - Unless you install the Integration Services (formerly virtual machine addons in Virtual Server 2005), the IDE drvier performs much worse in Hyper-V compared to Virtual Server 2005. Guest OS installations are horribly slow for this reason. If integration components are not available or installed on a Guest machine, you are going to suffer the same performance issue.

4 - Since the IDE performance without integration services is worse than Virtual Server 2005, and guest machines can't boot from SCSI, Linux virtual machines will greatly suffer unless stable synthetic drivers are available supporting major Linux distributions.

 

So, you should be fine with IDE drives as long as the OS is Windows and not Linux.

Edited March 15, 2010 by Guest

[Guest darosant]

Thank you very much for the information. It has been very useful.

David

[alexmvp]

Yeah no worries.....

 

So what do you think about Hyper-V vs. VMWare Home Server? Just curious which one you think is better since both are kinda free....

[Guest darosant]

This week I finished my first Hyper-V server built from scratch. I am using x64 W2K3SP2 with 2 cores and 2MB of Ram on the VS. I am very impressed with the performance over Virtual Server 2005. Even though I had no problems with 2003 server and VS2005, the performance improvement is outstanding. I haven't done anything with VMWare, but heard from a colleague that is pretty stable.

 

David

[Steve Krause]

This week I finished my first Hyper-V server built from scratch. I am using x64 W2K3SP2 with 2 cores and 2MB of Ram on the VS. I am very impressed with the performance over Virtual Server 2005. Even though I had no problems with 2003 server and VS2005, the performance improvement is outstanding. I haven't done anything with VMWare, but heard from a colleague that is pretty stable.

 

David

 

One of the largest performance improvements you might be seeing also is the newer processors which have Virtualization chipsets on them (Intel VT and AMD-V).

 

At work what were seeing with the newer Nehalem processors is about a full 3x improvement (as long as you have enough memory). Before we were getting around 20 VM's per host now were seeing about 50-60.