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Re: [Xen-users] GPLPV-drivers: size limit in "hard disk drivers" forvolu

To: James Harper <james.harper@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-users] GPLPV-drivers: size limit in "hard disk drivers" forvolumes?
From: Björn Schneider <bjoern.schneider@xxxxxxxxxxxxxxx>
Date: Tue, 25 Nov 2008 15:24:47 +0100
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I'm using the "Xen PV Drivers 0.9.12-pre4.exe" package on Windows 2008
Server SP1 32bit. The Dom0 is Ubuntu 8.04LTS amd64 with Ubuntu's kernel
2.6.24-21-xen and Xen 3.2.1-rc1-pre.

I've reduced the size down to a few sectors less than 1 Terabyte, and
now it works (couldn't pin it down exactly to the sector limit, as LVM2
uses 'LE units' which contain several sectors).

working size:       2147475456 sectors (1099507433472 bytes)
inoperative size:   2147483648    "    (1099511627776 bytes)

Interestingly, between 1 Terabyte and 2 Terabyte, the virtual disk shows
up, but without valid data. If you try to initialize the disk, Windows
returns the error that the disk would be write protected. If it's just
one "LE" below full 2 Terabyte, it says "unsupported operation" instead.

Hope that helps somehow...

Keep up the good work, anyway :)

   Björn Schneider

James Harper schrieb:
>> Hi,
>> I've encountered a strange behaviour of the block device PV driver: with
>> the Qemu-derived IO-emulation I can easily access both virtual drives of
>> 50 GByte and 2 Terabyte.
>>     When I activate GPLPV, only the 50G system partition shows up; the 2
>> TByte one is completely absent.
>> Is there a limit the GPLPV block driver can handle? -- everything else
>> seems to work fine... and yes, I need that 2TByte disk. It's a
>> fileserver :)
>>     I could of course try to split the disk and use the Windows volume
>> management to assemble it back -- but I don't know how to do that
>> exactly and it'd add another management layer. Which I don't want to.
>> Any ideas or maybe even a solution? :) But it's not that urgent, I can
>> still use the IO emulation until the system gets productive, which isn't
>> before January. And maybe even still then.
> What version of the drivers are you using, and also the exact sector count of 
> the disk?
> 2TByte is exactly 2^32 * 512 byte sectors, eg right on the limit of the 
> number of sectors a 32 bit integer can hold. I'll have to check, but I may 
> only be using the 32 bit SCSI commands... if you are actually just under 2TB 
> then this probably won't be the problem.
> James
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Björn Schneider, BSc.

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