Re: [Xen-users] Strange failures of Xen 4.3.1, PVHVM storage VM, iSCSI and Windows+GPLPV VM combination

[Kuba <kuba.0000@xxxxx>]

W dniu 2014-01-31 02:35, James Harper pisze:
> > I am trying to set up a following configuration:
> > 1. very simple Linux-based dom0 (Debian 7.3) with Xen 4.3.1 compiled
> > from sources,
> > 2. one storage VM (FreeBSD 10, HVM+PV) with SATA controller attached
> > using VT-d, exporting block devices via iSCSI to other VMs and physical
> > machines,
> > 3. one Windows 7 SP1 64 VM (HVM+GPLPV) with GPU passthrough (Quadro
> > 4000) installed on a block device exported from the storage VM (target
> > on the storage VM, initiator on dom0).
> >
> > Everything works perfectly (including PCI & GPU passthrough) until I
> > install GPLPV drivers on the Windows VM. After driver installation,
> > Windows needs to reboot, boots fine, displays a message that PV SCSI
> (a)
>
> > drivers were installed and needs to reboot again, and then cannot boot.
> > Sometimes it gets stuck at "booting from harddrive" in SeaBIOS,
> > sometimes BSODs with "unmountable boot volume" message. All of the
> > following I tried without GPU passthrough to narrow down the problem.
> >
> > The intriguing part is this:
> >
> > 1. If the storage VM's OS is Linux - it fails with the above symptoms.
> > 2. If the block devices for the storage VM come directly from dom0 (not
> > via pci-passthrough) - it fails.
> > 2. If the storage VM is an HVM without PV drivers (e.g. FreeBSD
> > 9.2-GENERIC) - it all works.
> > 3. If the storage VM's OS is Linux with kernel compiled without Xen
> > guest support - it works, but is unstable (see below).
> > 4. If the iSCSI target is on a different physical machine - it all works.
> > 5. If the iSCSI target is on dom0 itself - it works.
> > 6. If I attach the AHCI controller to the Windows VM and install
> > directly on the hard drive - it works.
> > 7. If the block device for Windows VM is a disk, partition, file, LVM
> > volume or even a ZoL's zvol (and it comes from a dom0 itself, without
> > iSCSI)- it works.
> >
> > If I install Windows and the GPLPV drivers on a hard drive attached to
> > dom0, Windows + GPLPV work perfectly. If I then give the same hard drive
> > as a block device to the storage VM and re-export it through iSCSI,
> (b)
>
> > Windows usually boots fine, but works unstable. And by unstable I mean
> > random read/write errors, sometimes programs won't start, ntdll.dll
> > crashes, and after couple reboots Windows won't boot (just like
> > mentioned above).
> >
> > The configurations I would like to achieve makes sense only with PV
> > drivers on both storage and Windows VM. All of the "components" seem to
> > work perfectly until all put together, so I am not really sure where the
> > problem is.
> >
> > I would be very grateful for any suggestions or ideas that could
> > possibly help to narrow down the problem. Maybe I am just doing
> > something wrong (I hope so). Or maybe there is a bug that shows itself
> > only in such a particular configuration (hope not)?
> I'm curious about prompting for the pvscsi drivers to be installed. Is this 
> definitely what it is asking for? Pvscsi for gplpv is removed in the latest 
> versions and suffered varying degrees of bitrot in earlier versions. If you 
> have the iscsi initiator in dom0 then exporting a block device to windows via 
> the normal vbd channel should be just fine.
>
> You've gone to great lengths to explain the various things you've tried, but I think I'm 
> a little confused on where the iscsi initiator is in the "doesn't work" 
> scenarios. I'm having a bit of an off day today so it's probably just me, but above I 
> have highlighted the two scenarios... could you fill me in on a few things:
>
> At (a) and (b), is the iscsi initiator in dom0, or are you actually booting 
> windows directly via iscsi?
>
> At (b), with latest debug build of gplpv, can you run debugview from 
> sysinternals.com and see if any interesting messages are displayed before 
> things fall in a heap?
>
> Are any strange logs shown in any of Win DomU, Dom0, or storage DomU?
>
> How big are your disks?
>
> Can you reproduce with only one vcpu?
>
> What bridge are you using? Openvswitch or traditional linux bridge?
>
> What MTU are you using on your storage network? If you are using Jumbo frames can 
> you go back to 1500 (or at least <= 4000)?
>
> Can you turn off scatter gather, Large Send Offload (GSO), and IP Checksum 
> offload on all the iscsi endpoints?
>
> Can you turn on data digest/checksum on iscsi? If all endpoints support it then 
> this would provide additional verification that none of the network packets are 
> getting corrupted.
>
> Would driver domain work in your scenario? Then the disk could be attached 
> directly from your storage DomU without accruing all the iscsi overhead. I'm 
> not up with the status of HVM, vbd, and driver domain so I don't know if this 
> is possible.
>
> More questions than answers. Sorry :)
>
> James
Dear James,

thank you for your questions - I really appreciate everything that may 
help me move closer to solving or isolating the problem.
I'll check what type of driver is used exactly - up until now I always 
just installed all drivers included in the package, I thought all of 
them were necessary. I'll try installing them without XenScsi.
Do you mean revisions > 1092:85b99b9795a6 by "the latest versions"? 
Which version should I use?
Forgive me if the descriptions were unclear. The initiator was always in 
dom0. I only moved the target to dom0 or a separate physical machine in 
(4) and (5). I didn't boot Windows directly from iSCSI (in fact I tried 
couple times, but had some problems with it, so I didn't mention it).
My "disks" (the block devices I dedicated to the Windows VM) were whole 
120GB and 240GB SSDs, ~100GB ZVOLs and 50GB LVM volumes.
I'm using traditional linux bridge. I didn't set MTUs explicitly, so I 
assume it's 1500, but I will verify this.
I'd love to use a storage driver domain, but the wiki says "It is not 
possible to use driver domains with pygrub or HVM guests yet". But the 
page is a couple of months old, maybe it's an outdated info? It surely 
is worth checking out.
I'll do my best to provide answers to the remaining questions as soon as 
possible. Thank you for so many ideas.
Best regards,
Kuba

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