From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladislav Bolkhovitin Subject: Re: [Stgt-devel] Question for pass-through target design Date: Wed, 23 May 2007 14:45:42 +0400 Message-ID: <46541B56.7000501@vlnb.net> References: <463B72F6.3000207@torque.net> <20070506053629P.fujita.tomonori@lab.ntt.co.jp> <463F36AC.3010207@vlnb.net> <20070507182837E.fujita.tomonori@lab.ntt.co.jp> <20070522195656.GD5758@austin.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from mail-relay-01.mailcluster.net ([85.249.135.242]:34476 "EHLO mail-relay-01.mailcluster.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758267AbXEWKpv (ORCPT ); Wed, 23 May 2007 06:45:51 -0400 In-Reply-To: <20070522195656.GD5758@austin.ibm.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: Robert Jennings Cc: FUJITA Tomonori , santil@us.ibm.com, stgt-devel@lists.berlios.de, scst-devel@lists.sourceforge.net, linux-scsi@vger.kernel.org Robert Jennings wrote: >>>>What I meant that is that the kernel tgt code (scsi_tgt*) receives >>>>SCSI commands from one lld and send them to another lld instead of >>>>sending them to user space. >>> >>>Although the approach of passing SCSI commands from a target LLD to an >>>initiator one without any significant interventions from the target >>>software looks to be nice and simple, you should realize how limited, >>>unsafe and illegal it is, since it badly violates SCSI specs. >> >>I think that 'implemented cleanly' means that one scsi_host is assigned >>to only one initiator. > > Vladislav listed a number of issues that are inherent in an implementation > that does not have a 1:1 relationship of initiators to targets. The vscsi > architecture defines the 1:1 relationship; it's imposible to have more > than one initiator per target. Just few small notes: 1. As I already wrote, complete 1:1 relationship isn't practically possible, because there is always a local access on the target (i.e. one more initiator) and you can't disable it on practice. 2. 1:1 relationship is a serious limitation for usage cases like an SPI tape library serving backup for several servers on an FC net. Vlad