From the information below, I would personally recommend using the following:
The PVSCSI controller will be the controller of the future so you may also want to keep this in mind. Of course you can make your own decisions. Most of the points made are desktop focused, however most will apply outside of a View environment.
IDE vs SCSI
Most people's main argument around reasons to not use IDE are;
BusLogic vs LSI Logic
If you have decided to use SCSI, you now have to decide on whether to use the BusLogic or LSI Logic SCSI controller.
*VMware's recommendation is to use the LSI Logic adapter. "The LSI Logic adapter has improved performance and works better with generic SCSI devices."
LSI Logic SAS
The default controller for a Windows 7 virtual machine is the LSI Logic SAS. There is no performance between this controller over the regular LSI Logic Parallel controller, so I therefore see no reason to change it.
It is worth noting, in Linux guests SCSI disk hotplug works better with SAS than with original parallel LSI. (You do not have to rescan the SCSI bus yourself to find a new device; on Windows you do not have to do rescan ever with ESX4.x, neither with LSI nor LSI-SAS)
Why not PVSCSI?
Virtual Desktops don't tend to have a really high I/O. Using the PVSCSI driver with low throughput workloads may introduce a small increase in latency.
Pre ESX 4.1 the PVSCSI adapter had only been recommended for VMDK's backed by fast (2,000+ IOPS) storage. Why? The PVSCSI driver only coalesces OIOs (Outstanding IOs) and not throughput (IOPS). What this means is; when the VM is requesting a lot of IO and the storage cannot deliver it, the PVSCSI driver is coalescing interrupts. Without the steady steam of IOs from the storage, there are no interrupts to coalesce. This can cause extra latency on low throughput environments.
The LSI Logic driver increases coalesce as OIO and IOPS increase. So if there is a low OIO and IOPS load no coalescing will occur, reducing latency.
Typically the case was:
However! In ESX 4.1 this issue explained above has been fixed. This means that the PVSCSI could perform as well as the LSI Logic driver with low throughput. I have yet to see any official performance test results. If you have already used PVSCSI adapters and are not seeing any performance problems, I wouldn't worry too much about making the change to LSI.
Summary
As you can see, there is a lot of Pro's and Con's to digest. I chose the SCSI LSI Logic controller for the following reasons:
What do you use on your site and why? Have I missed anything? let me know. I am interested to hear other peoples take on this, so please comment if you feel you have anything to add.
Sources
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View Comments
Good practical advice. Keep it up!
Nice info, Simon. Would love to be able to go to a standard of ESX 4.1 and PVSCSI for everything. Having different SCSI adapters for different VMs adds complexity.
Hi Simon,
Very nice post. I posted a similar post some time ago at http://www.vmdamentals.com/?p=1060
Results are pretty much the same; we must be doing something right ;)
Great to-the-point article. Hopefully this won't be an 'arguement' for too much longer!
great article, however, have you tried using scsi lsi logic with persistent data disks ? i have and the result is unpleasant. every time a recompose, refresh, or rebalance operation is executed the end user is prompted to install the driver for the scsi controller by the found new hardware wizard. multiply that by 250 or so users with no admin rights and you've got quite the headache.
Hi Chas, are you talking XP or WIN7?
If your golden image is setup properly then users should never get a prompt to install drivers. I'm guessing there is a miss configuration vs a problem with controller drivers in your os. Can you tell me how many iops the image is requesting and writing?
Simon,
I am running ESXi 5.0. I am using the "Create New VM" wizard to see what the default controller is based on the operating system I choose. Yes, 2008, 2008R2, Win7 default to the LSI Logic SAS. In choosing Windows 2003 32-bit or 64-bit VM, the wizard defaults to LSI Login Parallel. Before installation, do you believe it is safe or smart to change the controller to LSI Logic SAS for a Windows 2003 environment?
you need to change your blog's CSS. you need to do it now.
The new trend from companies allowing admins with novice computer skills full decision/change control access to corporate environments really worries me.
Nice commentary , Just to add my thoughts , if anyone requires a PBS Checklist of ADL , my business partner came across a sample version here
http://goo.gl/y8SfM6
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