Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756392Ab2BMMy0 (ORCPT ); Mon, 13 Feb 2012 07:54:26 -0500 Received: from mx1.redhat.com ([209.132.183.28]:41727 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752000Ab2BMMyY (ORCPT ); Mon, 13 Feb 2012 07:54:24 -0500 Message-ID: <4F3907EB.4030402@redhat.com> Date: Mon, 13 Feb 2012 14:54:03 +0200 From: Dor Laor Reply-To: dlaor@redhat.com User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:10.0) Gecko/20120131 Thunderbird/10.0 MIME-Version: 1.0 To: "Nicholas A. Bellinger" CC: Christian Borntraeger , James Bottomley , Paolo Bonzini , Christian Hoff , borntrae@linux.vnet.ibm.com, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, mst@redhat.com, rusty@rustcorp.com.au, Stefan Hajnoczi , target-devel Subject: Re: Pe: [PATCH v5 1/3] virtio-scsi: first version References: <4F30F4EE.4080607@redhat.com> <4F311154.9080407@de.ibm.com> <4F3119A0.7080005@redhat.com> <4F312492.1040002@de.ibm.com> <4F313526.2050907@redhat.com> <4F3390FB.80107@redhat.com> <1329077777.21613.60.camel@dabdike.int.hansenpartnership.com> <4F38B657.7060405@de.ibm.com> <4F38C27E.7030300@redhat.com> <1329136806.9333.383.camel@haakon2.linux-iscsi.org> In-Reply-To: <1329136806.9333.383.camel@haakon2.linux-iscsi.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3447 Lines: 89 On 02/13/2012 02:40 PM, Nicholas A. Bellinger wrote: > Hi Dor, James& Co, > > On Mon, 2012-02-13 at 09:57 +0200, Dor Laor wrote: >> On 02/13/2012 09:05 AM, Christian Borntraeger wrote: >>> On 12/02/12 21:16, James Bottomley wrote: >>>> Well, no-one's yet answered the question I had about why. >>> >>> Just to give one example from a different angle: >>> In the big datacenters tape libraries are still very important, and lots >>> of them have a scsi attachement. virtio-blk certainly is not the right >>> way to handle those. Furthermore it seems even pretty hard to craft >>> a virtio-tape since most of those libraries have vendor specific library >>> controls (via sg). We would need to duplicate scsi generic (hint, hint :-) >>> >>>> virtio-scsi seems to be a basic duplication of virtio-blk except that it seems to >>>> fix some problems virtio-blk has. Namely queue parameter discover, >>>> which virtio-blk doesn't seem to do. There may also be a reason to cut >>>> the stack lower down. Error handling is most often cited for this, but >>>> no-one's satisfactorily explaned why it's better to do error handling in >>>> the guest instead of the host. >>>> >>>> Could someone please explain to me why you can't simply fix virtio-blk? >>> >>> I dont think that virtio-scsi will replace virtio-blk everywhere. For non-scsi >>> block devices, image files or logical volumes virtio-blk seems to be the right >>> approach, I think. >> >> +1 >> >> virtio-scsi is superior w.r.t: >> - Device support: tapes, cdroms, other > > AFAICT any type of non TYPE_DISK struct scsi_device passthrough is going > to currently require virtio-scsi in order to work. > >> - Does guest-host mapped multipath > > The logic that comes with target_core_fabric_configfs.c and the native > target control plane gives a host-side (tcm_vhost) fabric driver generic > explict/implict ALUA multipath support by default. > > I think there are some interesting possibilities for paravirtualized > ALUA multipath.. 8-) > >> - Supports plenty of virtual disks mapped to the guest w/o need for a >> pci slot per each virtio-blk > > Ouch, virtio-blk lacks multi-lun per pci slot support..? Only if you use the pci multi-function option but that kills standard hot unplug > >> - offload fancy/new/sophisticated scsi commands from the guest to the >> storage array w/o need for qemu implementation. Example XCOPY. >> > > ... > >> There are some more goodies like ability to support windows guest >> clustering w/o hacky versions of scsi pass through over virtio-blk. >> virtio-blk is also a candidate to change the request based towards bio >> based implementation, so sticking to it does not buy us too much. >> > > MSFT cluster guests that require SPC-3 PR support can run today with > tcm_loop LLD SCSI LUNs + SG_IO/BSG + right megasas QEMU HBA emulation, > but I do agree this would be better served by virtio-scsi for guests > that require SPC-3 PR support or passthrough. > > --nab > > > > > > > > -- > To unsubscribe from this list: send the line "unsubscribe kvm" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/