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Re: [Qemu-devel] vpc size reporting problem
From: |
Chun Yan Liu |
Subject: |
Re: [Qemu-devel] vpc size reporting problem |
Date: |
Tue, 07 Jul 2015 00:34:02 -0600 |
>>> On 7/7/2015 at 02:19 PM, in message <559B6F79.237 : 102 : 21807>, Chun Yan
>>> Liu
wrote:
>
>
>>>> On 7/7/2015 at 02:03 PM, in message <address@hidden>, Peter Lieven
> <address@hidden> wrote:
> > Am 07.07.2015 um 07:59 schrieb Chun Yan Liu:
>> >
>> >>>> On 7/7/2015 at 01:50 PM, in message <address@hidden>, Peter Lieven
>> > <address@hidden> wrote:
>> >> Am 07.07.2015 um 03:50 schrieb Chun Yan Liu:
>> >>>>>> On 7/6/2015 at 06:42 PM, in message <address@hidden>, Peter Lieven
>> >>> <address@hidden> 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?
And imported to a Win7 guest on KVM as IDE device, it's also reported as
1024MB (not CHS value, CHS is 1023MB).
>
> 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.
>
>>
>> I had a look at the specs and in fact they more or less say: Use
>> current_size
>> and if you have an ATA controller derive the disk size from CHS.
>>
>> Peter
>>
>>
>>
>
- [Qemu-devel] vpc size reporting problem, Chun Yan Liu, 2015/07/06
- Re: [Qemu-devel] vpc size reporting problem, Peter Lieven, 2015/07/06
- Re: [Qemu-devel] vpc size reporting problem, Chun Yan Liu, 2015/07/06
- Re: [Qemu-devel] vpc size reporting problem, Peter Lieven, 2015/07/07
- Re: [Qemu-devel] vpc size reporting problem, Chun Yan Liu, 2015/07/07
- Re: [Qemu-devel] vpc size reporting problem, Peter Lieven, 2015/07/07
- Re: [Qemu-devel] vpc size reporting problem, Chun Yan Liu, 2015/07/07
- Re: [Qemu-devel] vpc size reporting problem, Peter Lieven, 2015/07/07
- Re: [Qemu-devel] vpc size reporting problem,
Chun Yan Liu <=
- Re: [Qemu-devel] vpc size reporting problem, Peter Lieven, 2015/07/07
- Re: [Qemu-devel] vpc size reporting problem, Chun Yan Liu, 2015/07/07