From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vladislav Bolkhovitin Subject: SCSI target and IO-throttling Date: Thu, 02 Mar 2006 19:21:56 +0300 Message-ID: <44071BA4.3030808@vlnb.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from out-relay-02.infobox.ru ([195.208.234.171]:54754 "EHLO out-relay-02.infobox.ru") by vger.kernel.org with ESMTP id S1751581AbWCBQWP (ORCPT ); Thu, 2 Mar 2006 11:22:15 -0500 Received: from in-relay-02.infobox.ru (in-relay-02.infobox.ru [195.208.234.235]) by out-relay-02.infobox.ru (Postfix) with ESMTP id A1E00400ECE6 for ; Thu, 2 Mar 2006 19:22:09 +0300 (MSK) Received: from [127.0.0.1] (cpe-72-225-37-244.rochester.res.rr.com [72.225.37.244]) (using SSLv3 with cipher RC4-MD5 (128/128 bits)) (No client certificate requested) by in-relay-02.infobox.ru (Postfix) with ESMTP id CBA85F00DECB for ; Thu, 2 Mar 2006 19:22:05 +0300 (MSK) Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org Hello Could anyone advice how a SCSI target device can IO-throttle its initiators, i.e. prevent them from queuing too many commands, please? I suppose, the best way for doing this is to inform the initiators about the maximum queue depth X of the target device, so any of the initiators will not send more than X commands. But I have not found anything similar to that on INQUIRY or MODE SENSE pages. Have I missed something? Just returning QUEUE FULL status doesn't look to be correct, because it can lead to out of order commands execution. Apparently, hardware SCSI targets don't suffer from queuing overflow and don't return all the time QUEUE FULL status, so the must be a way to do the throttling more elegantly. Regards, Vlad