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Re: [Xen-users] 4KB Sector Disks

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.


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


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