Re: [Xen-devel] Xen and 4K Sectors (was blkback and bcache)

[Pasi Kärkkäinen <pasik@xxxxxx>]

On Mon, Aug 13, 2012 at 01:25:07PM +0000, James Harper wrote:
> > 
> > I think the problem is definitely related to the 4K sector issue.
> > 
> > qemu appears to always present 512 byte sectors, thus only booting from a
> > 512 byte sector partition table. Once the PV drivers take over though it all
> > falls down because PV drivers are passed a 4K sector size and nothing
> > matches up anymore.
> > 
> > What is the solution here? Do I just tell windows that we have a 512 byte
> > sector and put up with the potential loss of performance?
> > 
> 
> I just came across this...
> 
> http://support.microsoft.com/kb/982018
> 
> I guess Windows doesn't support 4K disks after all, so I'll emulate 512 byte 
> sectors and fake whatever scsi interface is required to tell windows that the 
> disk is 4K but emulating 512 bytes.
> 

At least Linux reports:
/sys/block/<disk>/queue/logical_block_size=512
/sys/block/<disk>/queue/physical_block_size=4096

So I assume you need to set those somehow..

-- Pasi


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