Re: [Qemu-devel] vpc size reporting problem

[Peter Lieven <pl@kamp.de>]

Am 07.07.2015 um 08:19 schrieb Chun Yan Liu:
>
>>>> On 7/7/2015 at 02:03 PM, in message <559B6BBE.3050500@kamp.de>, Peter Lieven
> <pl@kamp.de> wrote:
>> Am 07.07.2015 um 07:59 schrieb Chun Yan Liu:
>>>>>> On 7/7/2015 at 01:50 PM, in message <559B68B2.5060402@kamp.de>, Peter Lieven
>>> <pl@kamp.de> wrote:
>>>> Am 07.07.2015 um 03:50 schrieb Chun Yan Liu:
>>>>>>>> On 7/6/2015 at 06:42 PM, in message <559A5B79.4010707@kamp.de>, Peter Lieven
>>>>> <pl@kamp.de> wrote:
>>>>>> Am 06.07.2015 um 11:44 schrieb Chun Yan Liu:
>>>>>>> While testing with a 1GB VHD file created on win7, found that the VHD file
>>>>>>> size reported on Windows is different from that is reported by qemu-img
>>>>>>> info or within a Linux KVM guest.
>>>>>>>
>>>>>>> Created a dynamic VHD file on win7, on Windows, it is reported 1024MB
>>>>>>> (2097152 sectors). But with qemu-img info or within a Linux KVM guest,
>>>>>>> it is reported 1023MB (2096640 sectors).
>>>>>>>
>>>>>>> The values in the footer_buf are as follows:
>>>>>>> creator_app: "win "
>>>>>>> cylinders: 0x820 (2080)
>>>>>>> heads: 0x10 (16)
>>>>>>> cyl/sec: 0x3f (63)
>>>>>>> current_size: 0x40000000 (1G)
>>>>>>>
>>>>>>> So, if using current_size, it's correct; but using CHS will get a smaller
>>>>>> size.
>>>>>>> Should we add a check in this case and use "current_size" instead of
>>>>>>> CHS?
>>>>>>       
>>>>>> As far as I remember the issue was and still is that there is no official
>>>>>> spec that says
>>>>>> use current_size in case A and CHS in case B.
>>>>> Understand.
>>>>>
>>>>>>       
>>>>>> If currrent_size is greater than CHS and Windows would use CHS (we don't
>>>>>> know that) we might run into issues if Qemu uses current_size. In this
>>>>>> cas we would write data beyond the end of the container (from Windows
>>>>>> perspective).
>>>>> That's right. The fact is in our testing we found Windows does not use CHS
>>>>> but current_size (from testing result), we create and get the VHD parted on
>>>>> Windows, then take the VHD file into Linux KVM guest, it fails to show
>>>> partition
>>>>> table (since the reported disk size is shrinking, some of the partitions
>>>> extend
>>>>> beyond the end of the disk).
>>>>     
>>>> Which version of Windows are you referring to?
>>> Tested with WS2012R2 and Win7.
>>   
>> Which storage driver?
> I'm not sure. See from "device management" -> "disk drive", it's named as "Msft
> virtual disk SCSI disk device", and from "storage controller", it has a separate
> controller named as "Microsoft VHD HBA". Anyway, seems not controlled by
> ATA/ATAPI.

Can you change that to IDE or ATA and check which size windows reports then?

Thanks,
Peter