Boot from Paravirtualized SCSI Adapter
From vSphere U1, VMware now support booting from a Paravirtualized SCSI adapter, why would you want to do this ? Well why not, check out the VMware Performance Blog where VMware have tested this adapter and shared their results.
VMware were able to achieve 350,000 I/O operations per second on a single vSphere host (ESX 4.0) and 3 virtual machines. From their findings the VMware Paravirtual SCSI (PVSCSI) adapter was able to achieve 12% more throughput with 18% less CPU cost compared to the LSI virtual adapter… Now you see why we should use it !
So in trying to test this the first thing I did was move one of my current virtual machines onto the adapter by clicking “edit settings” go to “SCSI controller 0” and click the change type button, from there you can select “VMware Paravirtual”.
When booting the VM you may find a slight issue though..
A ‘Blue Screen of Death’ welcomes you!
VMtools was installed and at the latest version (U1) but although the PVSCSI driver is shipped with VMtools it is not actually active until you add a PVSCSI adapter to the VM so to enable the PVSCSI driver for the boot device we need a slight bit of trickery….
1. With the VM powered off edit the settings and add an extra disk, just something small like 10MB, when choosing the ‘Virtual Device Node’ ensure you put it on another controller than any currently present, I chose SCSI 1:0 as I had no disks on the 1: node.
2. Once added you will also see that a new SCSI Controller has been added.
3. Select the SCSI Controller and click the “Change Type” button at the top Right, Select VMware Paravirtual , click OK and click OK again for the controller and disk to be added to the VM.
4. Power On the VM and log into the console, once logged in you will see that the controller and disk drivers are added to the OS.
And if you check in device manager you will see you now have a LSI Adapter and a VMware PVSCSI Adapter.
5. Now the drivers are installed shut down your VM
6. Go back into edit the settings and remove the disk we just added, this will automatically remove our extra controller too, whilst in the VM settings go to the original controller (SCSI Controller 0) and change the type to VMware Paravirtual as we did before.
7. Power back on the Virtual machine and check device manager, you should now only have the controllers we need.
Now you can reap the benefits of the extra speed !
As a note while we are on the subject don’t forget that if you build a VM from fresh using the Paravirtual SCSI Adapter you will need to hit F6 and select the drivers during the OS install.
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What windows version did you use? I tried these steps on 2003 R2, but didn’t have much success.
Lars
Excellent article – worked a treat. Cheers mate.
[...] SCSI devices – recently updated to allow booting, can allow higher-performance (greater throughput and lower CPU utilization) than the standard [...]
Luc added a script to his sight, but I’m wondering whether it will run in to the same BSOD issue you did (http://lucd.info/?p=1126). Let see if between the two of you, it can get scripted minus said issue. I’d work on it, but who am I kidding, you’d beat me to the punch =)
@dboftlp
Its actually an easy script, add a second disk with a paravitualised scsi adapter then turn off the vm, remove the second disk and adapter and power on the vm, job done !
Has anyone verified that you can still enable FT with a pvscsi adapter?
I just verified with VMware support that pvscsi adapters (as well as vmxnet adapters) are still not compatible with Fault Tolerance. Just a caveat to be aware of.
@Carl Skow
Thanks, thats useful to know.
[...] You might want to take advantage of the latest drivers for virtual SCSI adapters and virtual nic’s available in vSphere 4. To replace the buslogic parallel scsi adapter by the paravirtualized scsi adapter (PVSCSI). This adapter supports if Update 1 is used, also booting from the Paravirtual SCSI adapter. To replace the default SCSI adapter after the conversion has ended, follow the instructions published on http://www.virtu-al.net/2009/12/02/boot-from-paravirtualized-scsi-adapter/ [...]
[...] effet, comme le décrit Alan sur son blog, la solution la plus facile consiste à rebooter avec un disque temporaire sur un nouveau [...]
Here is another way to do it without dummy disk (driver injection) http://www.hypervisor.fr/?p=1764
[...] schönes HowTo mit Screenshots habe ich auf http://www.virtu-al.net gefunden. … other posts by [...]
There has been some follow up performance reports (http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1017652) that show that the pvSCSI adapter may not be the best choice for low IO VMs due to IO coalescing. And the thresholds are substantial.
“..The test results show that PVSCSI is better than LSI Logic, except under one condition–the virtual machine is performing less than 2,000 IOPS and issuing greater than 4 outstanding I/Os…”
Perhaps some perspective – you can expect that for every heavy email user, Exchange will typically generate 1/2 IOPS, so you will need 4000 heavy email users loaded up on an Exchange VM to really take advantage of the pvSCSI adapter.
Now those VMs that trickle feed IO, and with the adapter having to wait for IO to coalesce before dropping it on the (virtual) wire, pvSCSI may introduce additional IO latency.
pvSCSI is brilliant however, as with any tool, needs to be employed appropriately…
Average VMs will be fine with the LSI Logic
Thanks for the comment, that is really interesting, I am deploying soem Citrix boxes at the moment and whilst I havent done a direct side by side comparison it certainly seams faster to use from the user perspective, perhaps I will have to delve deeper.
I would like to share couple of things I ran into when I tried to convert boot disk to PVSCSI.
Same case has been reported to Vmware support.
The article is here.
http://geeksilver.wordpress.com/2010/06/21/upgrade-esx-3-5-to-vsphere-fixing-part-1-5/