On 15.03.2011, at 10:03, Stefan Hajnoczi wrote: > On Tue, Mar 15, 2011 at 7:47 AM, Alexander Graf <agraf@xxxxxxx> wrote: >> >> On 15.03.2011, at 08:09, Stefan Hajnoczi wrote: >> >>> On Mon, Mar 14, 2011 at 10:57 PM, Guido Winkelmann >>> <guido-kvml@xxxxxxxxxxxxxxxxx> wrote: >>>> On Monday 14 March 2011 20:32:23 Stefan Hajnoczi wrote: >>>>> On Mon, Mar 14, 2011 at 6:05 PM, Guido Winkelmann >>>>> >>>>> <guido-kvml@xxxxxxxxxxxxxxxxx> wrote: >>>>>> Does anybody have an idea what might cause this or what might be done >>>>>> about it? >>>>> >>>>> The lsi_scsi emulation code is incomplete. It does not handle some >>>>> situations like the ORDERED commands or message 0x0c. >>>>> >>>>> There is a patch to address the message 0xc issue, it has not been >>>>> applied to qemu.git or qemu-kvm.git yet: >>>>> http://patchwork.ozlabs.org/patch/63926/ >>>>> >>>>> Basically there is no one actively maintaining or reviewing patches >>>>> for the lsi53c895a SCSI controller. >>>> >>>> Does that mean that using the SCSI transport for virtual disks is officially >>>> unsupported or deprecated or that it should be? >>> >>> The LSI SCSI emulation in particular has not seen much attention. As >>> for the wider SCSI emulation there has been work over the past few >>> months so it's alive and being used. >>> >>>> Are things better with the IDE driver? >>> >>> IDE is commonly used for compatibility with guests that do not have >>> virtio-blk drivers. It should work fine although performance is poor >>> due to the IDE interface. >>> >>>>> virtio-blk works very will with Linux guests. Is there a reason you >>>>> need to use SCSI emulation instead of virtio-blk? >>>> >>>> I can probably use virtio-blk most of the time, I was just hoping to be able >>>> to virtualize a wider array of operating systems, like the *BSDs, >>>> (Open)Solaris, Windows, or even just some linux distributions whose installers >>>> don't anticipate KVM and thus don't support virtio-<anything>. >>> >>> Windows virtio-blk drivers are available and should be used: >>> http://www.linux-kvm.org/page/WindowsGuestDrivers/Download_Drivers >>> >>> BSD and Solaris don't ship with virtio-blk AFAIK. >> >> This is pretty much the gap that AHCI is trying to fill. It's a well-supported HBA that pretty much every OS supports, but is still simple enough to implement. Unfortunately, 0.14 ships without BIOS support for it, so you can't boot off an AHCI disk yet. But as of 0.15, AHCI is pretty much the adapter of choice for your use case. >> >> Please keep in mind that I didn't get FreeBSD rolling with AHCI emulation yet. OpenBSD works just fine. > > I think one missing AHCI feature was legacy PATA mode? Perhaps that > is a good GSoC project if you're willing to mentor it, Alex. I'm > thinking that with complete AHCI and legacy mode it would be a good > choice as the default non-virtio-blk disk interface. Or two be more precise: There are two different dimensions SATA / PATA IDE / AHCI The first is the link model - the type of connection the disk/cd-rom is connected to the hba with. The second is the OS interface. AHCI can handle SATA and PATA devices in AHCI mode. IIUC both link models also work in IDE (legacy) mode. The ICH-HBA can be BIOS configured to either operate in AHCI mode or in legacy mode, but not both at the same time. You can split between channels though. So you can have channels 1,2 operate through legacy while channels 3,4 go through AHCI. The same disk still can only be accessed either through IDE _or_ AHCI. Since we already have properly working PIIX3 IDE emulation code, I don't see the point in implementing ICH-7 AHCI IDE legacy compatibility mode. There are SATA controllers out there that apparently can expose the same disk through the legacy IDE interface and a faster SATA interface. I'm not sure any of those is AHCI compatible - the spec doesn't forbid you to do this. Alex -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
