From: torn5 Subject: Ext4 and scsi commands resubmission Date: Tue, 28 Dec 2010 11:41:58 +0100 Message-ID: <4D19BEF6.5010007@shiftmail.org> Mime-Version: 1.0 Content-Type: text/plain; format=flowed; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit To: linux-ext4@vger.kernel.org, "linux-scsi@vger.kernel.org" Return-path: Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org Hello all, in open-iscsi, when network connectivity is lost, scsi commands that were in-flight at the moment of disconnection are failed to the SCSI layer. These get resubmitted up to 5 times by the SCSI layer (or so is written in the open-iscsi docs) and after that they are held in the queue (device "blocked") until the network connection is restored. Now the question is: when SCSI resubmits commands to a device, I suppose they go to the end of the queue for the device, and not at the head like they were. Am I right? How do filesystems, and in particular ext4, react to that? I suppose the ordering goes awry, barriers cannot succeed in this way, especially if they were submitted as real SCSI barriers (i.e. without using flush + command + flush workaround) Thank you