[Qemu-devel] Help with Windows NT 4.0

[Qemu-devel] Help with Windows NT 4.0

[Programmingkid]

Lately I found out that Windows NT 4.0 seems to work well with the 486 and pentium processors. Using "-cpu 486" made installing it actually work. Now I am seeing another issue. When I boot Windows NT 4.0 I see this error message:

*** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000)
INACESSIBLE_BOOT_DEVICE

Would anyone know a way to solve this issue? 

Re: [Qemu-devel] Help with Windows NT 4.0

[Paolo Bonzini]

On 13/08/2017 21:13, Programmingkid wrote:
> Lately I found out that Windows NT 4.0 seems to work well with the
> 486 and pentium processors. Using "-cpu 486" made installing it
> actually work. Now I am seeing another issue. When I boot Windows NT
> 4.0 I see this error message:
> 
> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000) 
> INACESSIBLE_BOOT_DEVICE
> 
> Would anyone know a way to solve this issue?

Hervé is probably the best person to answer this question.  Maybe try
installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
scsi-cd,drive=cd").

Thanks,

Paolo

Re: [Qemu-devel] Help with Windows NT 4.0

[Mark Cave-Ayland]

On 14/08/17 07:51, Paolo Bonzini wrote:

> On 13/08/2017 21:13, Programmingkid wrote:
>> Lately I found out that Windows NT 4.0 seems to work well with the
>> 486 and pentium processors. Using "-cpu 486" made installing it
>> actually work. Now I am seeing another issue. When I boot Windows NT
>> 4.0 I see this error message:
>>
>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000) 
>> INACESSIBLE_BOOT_DEVICE
>>
>> Would anyone know a way to solve this issue?
> 
> Hervé is probably the best person to answer this question.  Maybe try
> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
> scsi-cd,drive=cd").

FWIW I used to run NT 4.0 in QEMU 0.9.1 without too many problems,
(although every so often the mouse would go crazy and it would require a
reboot). The only thing I needed to do was install updated VGA drivers
from http://www.bearwindows.boot-land.net/vbemp.htm in order to prevent
issues with the mouse pointer not displaying correctly.

I'm also fairly sure that was with a single -hda on the command line, so
it might be useful to go back quite far back in time to figure out what
changed.


ATB,

Mark.

Re: [Qemu-devel] Help with Windows NT 4.0

[Programmingkid]

> On Aug 14, 2017, at 3:18 AM, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk> wrote:
> 
> On 14/08/17 07:51, Paolo Bonzini wrote:
> 
>> On 13/08/2017 21:13, Programmingkid wrote:
>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>> actually work. Now I am seeing another issue. When I boot Windows NT
>>> 4.0 I see this error message:
>>> 
>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000) 
>>> INACESSIBLE_BOOT_DEVICE
>>> 
>>> Would anyone know a way to solve this issue?
>> 
>> Hervé is probably the best person to answer this question.  Maybe try
>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>> scsi-cd,drive=cd").
> 
> FWIW I used to run NT 4.0 in QEMU 0.9.1 without too many problems,
> (although every so often the mouse would go crazy and it would require a
> reboot). The only thing I needed to do was install updated VGA drivers
> from http://www.bearwindows.boot-land.net/vbemp.htm in order to prevent
> issues with the mouse pointer not displaying correctly.
> 
> I'm also fairly sure that was with a single -hda on the command line, so
> it might be useful to go back quite far back in time to figure out what
> changed.
> 
> 
> ATB,
> 
> Mark.

Thanks for the info. Trying to build 0.9.1 is going to be challenging. It requires GCC 3.x. 

Re: [Qemu-devel] Help with Windows NT 4.0

[Programmingkid]

> On Aug 14, 2017, at 3:18 AM, Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk> wrote:
> 
> On 14/08/17 07:51, Paolo Bonzini wrote:
> 
>> On 13/08/2017 21:13, Programmingkid wrote:
>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>> actually work. Now I am seeing another issue. When I boot Windows NT
>>> 4.0 I see this error message:
>>> 
>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000) 
>>> INACESSIBLE_BOOT_DEVICE
>>> 
>>> Would anyone know a way to solve this issue?
>> 
>> Hervé is probably the best person to answer this question.  Maybe try
>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>> scsi-cd,drive=cd").
> 
> FWIW I used to run NT 4.0 in QEMU 0.9.1 without too many problems,
> (although every so often the mouse would go crazy and it would require a
> reboot). The only thing I needed to do was install updated VGA drivers
> from http://www.bearwindows.boot-land.net/vbemp.htm in order to prevent
> issues with the mouse pointer not displaying correctly.
> 
> I'm also fairly sure that was with a single -hda on the command line, so
> it might be useful to go back quite far back in time to figure out what
> changed.
> 
> 
> ATB,
> 
> Mark.

I encountered the mouse problem also. It acts very similar to what we saw with Mac OS 9 not too long ago. 

Re: [Qemu-devel] Help with Windows NT 4.0

[Programmingkid]

> On Aug 14, 2017, at 2:51 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> On 13/08/2017 21:13, Programmingkid wrote:
>> Lately I found out that Windows NT 4.0 seems to work well with the
>> 486 and pentium processors. Using "-cpu 486" made installing it
>> actually work. Now I am seeing another issue. When I boot Windows NT
>> 4.0 I see this error message:
>> 
>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000) 
>> INACESSIBLE_BOOT_DEVICE
>> 
>> Would anyone know a way to solve this issue?
> 
> Hervé is probably the best person to answer this question.  Maybe try
> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
> scsi-cd,drive=cd").
> 
> Thanks,
> 
> Paolo

Thanks for the help. Unfortunately trying to boot from the install CD leads to the INACCESSIBLE_BOOT_DEVICE error when using SCSI. 

Re: [Qemu-devel] Help with Windows NT 4.0

[Paolo Bonzini]

On 15/08/2017 20:46, Programmingkid wrote:
> 
>> On Aug 14, 2017, at 2:51 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>> On 13/08/2017 21:13, Programmingkid wrote:
>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>> actually work. Now I am seeing another issue. When I boot Windows NT
>>> 4.0 I see this error message:
>>>
>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000) 
>>> INACESSIBLE_BOOT_DEVICE
>>>
>>> Would anyone know a way to solve this issue?
>>
>> Hervé is probably the best person to answer this question.  Maybe try
>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>> scsi-cd,drive=cd").
>>
>> Thanks,
>>
>> Paolo
> 
> Thanks for the help. Unfortunately trying to boot from the install CD leads to the INACCESSIBLE_BOOT_DEVICE error when using SCSI. 

Try with 0.12.

Paolo

Re: [Qemu-devel] Help with Windows NT 4.0

[G 3]

On Aug 15, 2017, at 6:27 PM, Paolo Bonzini wrote:

> On 15/08/2017 20:46, Programmingkid wrote:
>>
>>> On Aug 14, 2017, at 2:51 AM, Paolo Bonzini <pbonzini@redhat.com>  
>>> wrote:
>>>
>>> On 13/08/2017 21:13, Programmingkid wrote:
>>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>>> actually work. Now I am seeing another issue. When I boot  
>>>> Windows NT
>>>> 4.0 I see this error message:
>>>>
>>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000)
>>>> INACESSIBLE_BOOT_DEVICE
>>>>
>>>> Would anyone know a way to solve this issue?
>>>
>>> Hervé is probably the best person to answer this question.  Maybe  
>>> try
>>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>>> scsi-cd,drive=cd").
>>>
>>> Thanks,
>>>
>>> Paolo
>>
>> Thanks for the help. Unfortunately trying to boot from the install  
>> CD leads to the INACCESSIBLE_BOOT_DEVICE error when using SCSI.
>
> Try with 0.12.
>
> Paolo

Here is what I tried and the results:
QEMU	Windows NT 4.0 Status
---------	--------------------------------
0.9.1	Works
0.10.2	Freezes at the blue startup screen
0.13.0	Freezes at the blue startup screen
1.0.1	Freezes at the blue startup screen

I'm working to find if a single commit broke QEMU's Windows NT 4.0  
compatibility. I think its possible the BIOS might be the issue. 

Re: [Qemu-devel] Help with Windows NT 4.0

[G 3]

On Aug 15, 2017, at 6:27 PM, Paolo Bonzini wrote:

> On 15/08/2017 20:46, Programmingkid wrote:
>>
>>> On Aug 14, 2017, at 2:51 AM, Paolo Bonzini <pbonzini@redhat.com>  
>>> wrote:
>>>
>>> On 13/08/2017 21:13, Programmingkid wrote:
>>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>>> actually work. Now I am seeing another issue. When I boot  
>>>> Windows NT
>>>> 4.0 I see this error message:
>>>>
>>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000)
>>>> INACESSIBLE_BOOT_DEVICE
>>>>
>>>> Would anyone know a way to solve this issue?
>>>
>>> Hervé is probably the best person to answer this question.  Maybe  
>>> try
>>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>>> scsi-cd,drive=cd").
>>>
>>> Thanks,
>>>
>>> Paolo
>>
>> Thanks for the help. Unfortunately trying to boot from the install  
>> CD leads to the INACCESSIBLE_BOOT_DEVICE error when using SCSI.
>
> Try with 0.12.

After doing a lot of bisecting I found a patch that did break Windows  
NT 4.0 compatibility long ago. Not sure if it is the problem we face  
today. This is it:

commit 2bec46dc97571a3c34b18fe4ca198e7bfbdca41f
Author: aliguori <aliguori@c046a42c-6fe2-441c-8c8c-71466251a162>
Date:   Mon Nov 24 20:21:41 2008 +0000

     vga optimization (Glauber Costa)

     Hypervisors like KVM perform badly while doing mmio on
     a loop, because it'll generate an exit on each access.
     This is the case with VGA, which results in very bad
     performance.

     In this patch, we map the linear frame buffer as RAM,
     make sure it has dirty region tracking enabled, and then
     just let the region to be written.

Re: [Qemu-devel] Help with Windows NT 4.0

[Programmingkid]

> On Aug 15, 2017, at 6:27 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
> 
> On 15/08/2017 20:46, Programmingkid wrote:
>> 
>>> On Aug 14, 2017, at 2:51 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>> 
>>> On 13/08/2017 21:13, Programmingkid wrote:
>>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>>> actually work. Now I am seeing another issue. When I boot Windows NT
>>>> 4.0 I see this error message:
>>>> 
>>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000) 
>>>> INACESSIBLE_BOOT_DEVICE
>>>> 
>>>> Would anyone know a way to solve this issue?
>>> 
>>> Hervé is probably the best person to answer this question.  Maybe try
>>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>>> scsi-cd,drive=cd").
>>> 
>>> Thanks,
>>> 
>>> Paolo
>> 
>> Thanks for the help. Unfortunately trying to boot from the install CD leads to the INACCESSIBLE_BOOT_DEVICE error when using SCSI. 
> 
> Try with 0.12.
> 
> Paolo

I finally figured out why I was seeing the INACESSIBLE_BOOT_DEVICE error. It was because of the qcow2 image format. As soon as I switched to the qcow format, the error disappeared. 

Re: [Qemu-devel] Help with Windows NT 4.0

[Artyom Tarasenko]

On Fri, Aug 18, 2017 at 6:31 AM, Programmingkid
<programmingkidx@gmail.com> wrote:
>
>> On Aug 15, 2017, at 6:27 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>
>> On 15/08/2017 20:46, Programmingkid wrote:
>>>
>>>> On Aug 14, 2017, at 2:51 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>>
>>>> On 13/08/2017 21:13, Programmingkid wrote:
>>>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>>>> actually work. Now I am seeing another issue. When I boot Windows NT
>>>>> 4.0 I see this error message:
>>>>>
>>>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000)
>>>>> INACESSIBLE_BOOT_DEVICE
>>>>>
>>>>> Would anyone know a way to solve this issue?
>>>>
>>>> Hervé is probably the best person to answer this question.  Maybe try
>>>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>>>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>>>> scsi-cd,drive=cd").
>>>>
>>>> Thanks,
>>>>
>>>> Paolo
>>>
>>> Thanks for the help. Unfortunately trying to boot from the install CD leads to the INACCESSIBLE_BOOT_DEVICE error when using SCSI.
>>
>> Try with 0.12.
>>
>> Paolo
>
> I finally figured out why I was seeing the INACESSIBLE_BOOT_DEVICE error. It was because of the qcow2 image format. As soon as I switched to the qcow format, the error disappeared.

That's weird. The image format is not guest visible. Probably you are
hitting some sort of timing issue.


-- 
Regards,
Artyom Tarasenko

SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu

Re: [Qemu-devel] Help with Windows NT 4.0

[Programmingkid]

> On Aug 18, 2017, at 4:46 AM, Artyom Tarasenko <atar4qemu@gmail.com> wrote:
> 
> On Fri, Aug 18, 2017 at 6:31 AM, Programmingkid
> <programmingkidx@gmail.com> wrote:
>> 
>>> On Aug 15, 2017, at 6:27 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>> 
>>> On 15/08/2017 20:46, Programmingkid wrote:
>>>> 
>>>>> On Aug 14, 2017, at 2:51 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>>> 
>>>>> On 13/08/2017 21:13, Programmingkid wrote:
>>>>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>>>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>>>>> actually work. Now I am seeing another issue. When I boot Windows NT
>>>>>> 4.0 I see this error message:
>>>>>> 
>>>>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000)
>>>>>> INACESSIBLE_BOOT_DEVICE
>>>>>> 
>>>>>> Would anyone know a way to solve this issue?
>>>>> 
>>>>> Hervé is probably the best person to answer this question.  Maybe try
>>>>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>>>>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>>>>> scsi-cd,drive=cd").
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> Paolo
>>>> 
>>>> Thanks for the help. Unfortunately trying to boot from the install CD leads to the INACCESSIBLE_BOOT_DEVICE error when using SCSI.
>>> 
>>> Try with 0.12.
>>> 
>>> Paolo
>> 
>> I finally figured out why I was seeing the INACESSIBLE_BOOT_DEVICE error. It was because of the qcow2 image format. As soon as I switched to the qcow format, the error disappeared.
> 
> That's weird. The image format is not guest visible. Probably you are
> hitting some sort of timing issue.
> 
> 
> -- 
> Regards,
> Artyom Tarasenko
> 
> SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu

I'm not sure how timing is involved but I'm pretty sure I've heard about guests having problems with the qcow2 format in the past. 

Re: [Qemu-devel] Help with Windows NT 4.0

[John Snow]

On 08/18/2017 09:36 AM, Programmingkid wrote:
> 
>> On Aug 18, 2017, at 4:46 AM, Artyom Tarasenko <atar4qemu@gmail.com> wrote:
>>
>> On Fri, Aug 18, 2017 at 6:31 AM, Programmingkid
>> <programmingkidx@gmail.com> wrote:
>>>
>>>> On Aug 15, 2017, at 6:27 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>>
>>>> On 15/08/2017 20:46, Programmingkid wrote:
>>>>>
>>>>>> On Aug 14, 2017, at 2:51 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>>>>
>>>>>> On 13/08/2017 21:13, Programmingkid wrote:
>>>>>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>>>>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>>>>>> actually work. Now I am seeing another issue. When I boot Windows NT
>>>>>>> 4.0 I see this error message:
>>>>>>>
>>>>>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000)
>>>>>>> INACESSIBLE_BOOT_DEVICE
>>>>>>>
>>>>>>> Would anyone know a way to solve this issue?
>>>>>>
>>>>>> Hervé is probably the best person to answer this question.  Maybe try
>>>>>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>>>>>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>>>>>> scsi-cd,drive=cd").
>>>>>>
>>>>>> Thanks,
>>>>>>
>>>>>> Paolo
>>>>>
>>>>> Thanks for the help. Unfortunately trying to boot from the install CD leads to the INACCESSIBLE_BOOT_DEVICE error when using SCSI.
>>>>
>>>> Try with 0.12.
>>>>
>>>> Paolo
>>>
>>> I finally figured out why I was seeing the INACESSIBLE_BOOT_DEVICE error. It was because of the qcow2 image format. As soon as I switched to the qcow format, the error disappeared.
>>
>> That's weird. The image format is not guest visible. Probably you are
>> hitting some sort of timing issue.
>>
>>
>> -- 
>> Regards,
>> Artyom Tarasenko
>>
>> SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu
> 
> I'm not sure how timing is involved but I'm pretty sure I've heard about guests having problems with the qcow2 format in the past. 
> 

If the qcow2 driver in QEMU is written correctly, it should be 100%
invisible to guests. There should be no actual way to determine in any
way that qcow2 is being used.

Either the qcow2 driver is broken (unlikely), or the way in which the
qcow2 driver is written is exposing race conditions or other timing
problems in either the qcow2 driver, the guest, or both.

The odds of this being a "qcow2 problem" are pretty slim.

--js

Re: [Qemu-devel] Help with Windows NT 4.0

[Programmingkid]

> On Aug 18, 2017, at 3:23 PM, John Snow <jsnow@redhat.com> wrote:
> 
> 
> 
> On 08/18/2017 09:36 AM, Programmingkid wrote:
>> 
>>> On Aug 18, 2017, at 4:46 AM, Artyom Tarasenko <atar4qemu@gmail.com> wrote:
>>> 
>>> On Fri, Aug 18, 2017 at 6:31 AM, Programmingkid
>>> <programmingkidx@gmail.com> wrote:
>>>> 
>>>>> On Aug 15, 2017, at 6:27 PM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>>> 
>>>>> On 15/08/2017 20:46, Programmingkid wrote:
>>>>>> 
>>>>>>> On Aug 14, 2017, at 2:51 AM, Paolo Bonzini <pbonzini@redhat.com> wrote:
>>>>>>> 
>>>>>>> On 13/08/2017 21:13, Programmingkid wrote:
>>>>>>>> Lately I found out that Windows NT 4.0 seems to work well with the
>>>>>>>> 486 and pentium processors. Using "-cpu 486" made installing it
>>>>>>>> actually work. Now I am seeing another issue. When I boot Windows NT
>>>>>>>> 4.0 I see this error message:
>>>>>>>> 
>>>>>>>> *** STOP: 0x0000007B (0x807A8610,0x00000000,0x00000000,0x00000000)
>>>>>>>> INACESSIBLE_BOOT_DEVICE
>>>>>>>> 
>>>>>>>> Would anyone know a way to solve this issue?
>>>>>>> 
>>>>>>> Hervé is probably the best person to answer this question.  Maybe try
>>>>>>> installing it with SCSI disks ("-drive if=scsi,id=hd,file=... -drive
>>>>>>> if=scsi,id=cd,file=... -device lsi -device scsi-hd,drive=hd -device
>>>>>>> scsi-cd,drive=cd").
>>>>>>> 
>>>>>>> Thanks,
>>>>>>> 
>>>>>>> Paolo
>>>>>> 
>>>>>> Thanks for the help. Unfortunately trying to boot from the install CD leads to the INACCESSIBLE_BOOT_DEVICE error when using SCSI.
>>>>> 
>>>>> Try with 0.12.
>>>>> 
>>>>> Paolo
>>>> 
>>>> I finally figured out why I was seeing the INACESSIBLE_BOOT_DEVICE error. It was because of the qcow2 image format. As soon as I switched to the qcow format, the error disappeared.
>>> 
>>> That's weird. The image format is not guest visible. Probably you are
>>> hitting some sort of timing issue.
>>> 
>>> 
>>> -- 
>>> Regards,
>>> Artyom Tarasenko
>>> 
>>> SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu
>> 
>> I'm not sure how timing is involved but I'm pretty sure I've heard about guests having problems with the qcow2 format in the past. 
>> 
> 
> If the qcow2 driver in QEMU is written correctly, it should be 100%
> invisible to guests. There should be no actual way to determine in any
> way that qcow2 is being used.

That is what I thought.

> Either the qcow2 driver is broken (unlikely), or the way in which the
> qcow2 driver is written is exposing race conditions or other timing
> problems in either the qcow2 driver, the guest, or both.

Interesting idea.

> 
> The odds of this being a "qcow2 problem" are pretty slim.
> 
> --js

To anyone who wishes to recreate this test here is what you need to do.

Download this iso:
https://archive.org/download/Microsoft_Windows_NT_Workstation_4.0_Microsoft_1996/Microsoft%20Windows%20NT%20Workstation%20(4.0)%20(Microsoft)%20(1996).iso

Create the qcow hard drive image file:
qemu-img create -f qcow qcowtest.qcow 4G

Create the qcow2 hard drive image file:
qemu-img create -f qcow2 qcow2test.qcow2 4G

Install Windows NT 4.0 for each hard drive image file type:
qemu-system-i386 -cpu pentium -vga cirrus -hda qcowtest.qcow -boot c
-cdrom <Windows NT 4.0 iso file>

qemu-system-i386 -cpu pentium -vga cirrus -hda qcow2test.qcow2 -boot c
-cdrom <Windows NT 4.0 iso file>

The actual installation for Windows NT 4.0 only takes about 5 minutes to do, so it should be an easy test to do. Once done installing and setting up Windows, try quitting and relaunching QEMU for each image format. 

Windows NT Workstation 4.0 CD-KEY: 30495-0006276-08164 

Please let us know your results.