Re: [Xen-users] 4KB Sector Disks

[Gordan Bobic <gordan@xxxxxxxxxx>]

On Thu, 6 Jun 2013 09:58:51 +0100, Ian Campbell 
<Ian.Campbell@xxxxxxxxxx> wrote:
> On Wed, 2013-06-05 at 07:47 +0100, Gordan Bobic wrote:
> > I just thought I'd mention this because it turned out to be the 
> > cause of
> > disk I/O performance issues I've been having. For the 
> > arhchive/search
> > engines of nothing else.
> >
> > Setup:
> >
> > Storage server (Linux):
> > 1) ZFS zvol backed images, ZFS configured for 4KB sector disks
> > 2) IETD iSCSI server
> >
> > dom0 (Linux):
> > 3) Open-iSCSI client (Linux)
> >
> > domU is Windows.
> Does Windows know about 4k sectors, or does that end at #3? I can
> imagine that doing a read/modify/write for each 512 bytes written 
> would
> kill performance.
Good question. I don't know, but it can see all the space on the 
volume,
and there is no 512B emulation going on at any point up to and 
including
point #3. The sectors, at lest to dom0, show up as 4096 bytes, both
physical and logical.

> You mention qemu so I guess this is using emulated IDE -- I'd be very
> surprised if that supported anything other than 512b sectors, perhaps
> the upstream qemu version might but I doubt the Xen traditional fork
> does. I don't know if it is possible to get PV drivers into the 
> Windows
> installer super early but if it was (driver disk?) that would be 
> useful,
> otherwise installing them ASAP after initial install would seem wise.
I'm not sure if it "supports" anything other than 512B sectors, but it
seemed to work without any errors/corruption, albeit very slowly.

Installing PV drivers resulted in BSODs during booting.

Ideally, I'm hoping to get the domU booting to an iSCSI share directly
via the PCI-passthrough NIC, thus avoiding the need for PV drivers
alltogether.

Gordan

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