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VMware Tools & Paravirtual SCSI Controller

Following best practices, I've been using the VMware Paravirtual SCSI controller for my disks.  I am able to create the templates by attaching the floppy which holds the driver for the disk, then i proceed as normal.  Eventually i'll disconnect and disable floppy drives as well.  I've had no issues with this configuration until now...  

In an effort to diagnose why my VMs cannot perform a quiesced snapshot manually, I have tried to uninstall VMware Tools, reboot, then reinstall VMware Tools.  Seems easy enough and very straight-forward (especially since it did once boot without tools during the creation of the VM).  Once I reboot my VM without Tools it does not come back online.  It gives me a "Stop Error:  Inaccessible Boot Device."

I've tried swapping the disk to an LSI Logic Controller to access command line.  During this time I have tried to assign the correct volume letters, copying driver files to the c:\ (even though it can't yet boot), and using bootrec commands to rebuild.  There is no system restore option available on the servers.

Since it has once booted without Tools, I suspect that when I uninstalled Tools it also removed a driver/driver reference within a boot file.  Does anybody know where that driver(s) is located, I suspect its on the system reserved partition so I can copy the files back?  Or if you know of a way to resolve this stop error that would also be great.  I should be able to uninstall VMware tools without a booting issue.

NOTE:  Most posts I've found on this error, people simply rebuilt but that doesn't solve my problem of being able to uninstall my tools.
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jmachado81
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jmachado81
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
In an effort to diagnose why my VMs cannot perform a quiesced snapshot manually, I have tried to uninstall VMware Tools, reboot, then reinstall VMware Tools.  Seems easy enough and very straight-forward (especially since it did once boot without tools during the creation of the VM).  Once I reboot my VM without Tools it does not come back online.  It gives me a "Stop Error:  Inaccessible Boot Device."

Probably not the reason for Snapshot failure!

Anyway, the driver has not been installed into the system drivers. e.g. does not suggest to me the VM has been created correctly using the additional drivers.

Uninstalling VMware Tools removes VMware Tools and drivers, but it should not remove drivers which are installed in the drivers hive...

you should be able to check the inf files.

As a fyi, performance of the paravirtual driver is very similar to other drivers, and depends on workload.
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jmachado81Author Commented:
I found that not having VSS service tools feature installed caused some of my quiesce failures.  It was recommended by support to reinstall the tools to possibly resolve the rest however I've ran into this issue.  THe pvscsi.sys file does exist in the c:\windows\system32\drivers directory.  Is that the directory you're speaking of?

If you feel the driver wasn't correctly installed, what is the correct process?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
VMware Tools is NOT optional, and you must have VSS - VMware Tools installed if you want to have a correctly quicesed file system. BUT you don't have to and can snapshot a machine, and have a crash consistent VM, which does not quicesed the file system, where snapshot fails because of VSS sync driver

BUT VSS can cause issues with VM, and VMs with high CPU, no enough resources, slow datastores of HIGH transactions in the VM!

It is odd, that tools removes the driver, anyway don't remove tools it's required, or re-install and do not install the VSS driver!

the driver should be in the drivers folder.

if you have fed the driver through a floppy disk, as part of the OS build, It is odd that VMware Tools uninstall should remove it...
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jmachado81Author Commented:
Andrew,  I agree that a form of VMware Tools are required to run as they include network, display, etc drivers that are needed to communicate with other systems.  However there are cases where a VMware Tools installation becomes corrupt and must be manually removed then rebooted to clean it up, which should without a doubt be possible.  It's like taking an engine out of a car to rebuild it and the entire car blows up.
 I have also tried to change over a healthy paravirtual disk (without touching Tools) to LSI Logic SAS controller and the VM won't boot.

Do you know if this is the typical behavior of a paravirtual disk configuration? Can't uninstall Tools and can't migrate the disk to another type of controller without rebuilding the entire VM.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Andrew,  I agree that a form of VMware Tools are required to run as they include network, display, etc drivers that are needed to communicate with other systems.  However there are cases where a VMware Tools installation becomes corrupt and must be manually removed then rebooted to clean it up, which should without a doubt be possible.  It's like taking an engine out of a car to rebuild it and the entire car blows up.

we've never seen a VMware Tools installation corrupted, we've seen issues with VSS driver. Requiring a re-install/remove etc

But we've not seen it calls issue with system drivers.

Changing storage controllers if not done correctly, will result in Inaccessible Boot error message and BSOD and Stop 0x70 etc e.g. you cannot just change the type in settings, and hope it will boot.

What is the VM OS ?
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jmachado81Author Commented:
The OS is primarily 2016 but there are a few 2012 R2 OS using the paravirtual driver in my environment.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
which OS would you like me to try ?

also what is your host OS version ?

we will see if we can reproduce here in the lab.
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jmachado81Author Commented:
Try with Guest OS 2016 Std and the host is VMware ESXi, 6.0.0, 6765062 (vCenter 6.5).  Thanks.
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Okay, I have a Guest OS - 2016 Standard with VMware Paravirtual Driver installed as BOOT device.

after uninstalling VMware Tools it removes the drivers from Program Files\Common Files\VMware\drivers

but it does not remove the driver from System32\drivers.

BUT on reboot, the OS failed to start inaccessible BOOT disk.

and the driver is GONE.

So VMware Tools does tamper and remove the PVSCSI.SYS driver from the OS, which is a bit naughty!

So issue confirmed.

also documented here

https://www.peppercrew.nl/index.php/2017/10/how-to-reinstall-vmware-tools-on-a-paravirtual-vm/
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jmachado81Author Commented:
That article is great.  Thank you.

If i decide that I don't want my admins to undertake these additional steps, would I simply leave it on the LSI Logic controller and remove the paravirtual controller without causing any known issues?  Would you recommend the LSI Logic SaS controller as the better controller option?
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Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
Yes, we see no reason to use Paravirtual, unless you have a specific DB workload.
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