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

[James Harper <james.harper@xxxxxxxxxxxxxxxx>]

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?

Thanks

James

> -----Original Message-----
> From: xen-devel-bounces@xxxxxxxxxxxxx [mailto:xen-devel-
> bounces@xxxxxxxxxxxxx] On Behalf Of James Harper
> Sent: Monday, 13 August 2012 5:17 PM
> To: xen-devel@xxxxxxxxxxxxx
> Subject: [Xen-devel] blkback and bcache
> 
> I'm having trouble using blkback under gplpv when the disk is on top of a
> bcache device. My devices are layered as follows:
> 
> /dev/sd[ab]
> md0 (RAID1)
> bcache
> lvm
> 
> It seems that bcache presents a 4K sector size to Linux, which is then
> reflected by lvm and in turn blkback.
> 
> Obviously GPLPV isn't handling 4K sectors correctly... any suggestions as to
> what I might need to do to make this work properly? As a last resort I should
> be able to fake 512 byte sectors to Windows but would prefer that Windows
> knew it was dealing with a device with 4K sectors underneath.
> 
> Thanks
> 
> James
> 
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