From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pat LaVarre Subject: zero block writes Date: 14 Oct 2003 13:48:27 -0600 Sender: linux-scsi-owner@vger.kernel.org Message-ID: <1066160907.3501.9.camel@patehci2> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Return-path: Received: from email-out2.iomega.com ([147.178.1.83]:24226 "EHLO email.iomega.com") by vger.kernel.org with ESMTP id S261670AbTJNTso (ORCPT ); Tue, 14 Oct 2003 15:48:44 -0400 Received: from royntex01.iomegacorp.com (unknown [147.178.90.120]) by email.iomega.com (Postfix) with ESMTP id 6EEE617A8 for ; Tue, 14 Oct 2003 13:48:43 -0600 (MDT) List-Id: linux-scsi@vger.kernel.org To: linux-scsi@vger.kernel.org $ $ sg_dd of=/dev/sg0 if=/dev/null bs=2k count=1 0+0 records in 0+0 records out $ cdb trace tells me this sg utils idiom assaults the device with a zero block write, specifically: ... usb-storage: Command WRITE_10 (10 bytes) usb-storage: 2a 00 00 00 00 00 00 00 00 00 usb-storage: Bulk command S 0x43425355 T 0x1e Trg 0 LUN 0 L 0 F 0 CL 10 ... I wonder if any of you find this sg utils factoid ineffably interesting, as I do? I know I have a personal history of pain with the scsi folk who dispute the t10 claim that the cdb x 0A 00:00:00 00 00 means write out x100 blocks rather than zero and/or while yet that the cdb x 2A 00 00:00:00:00 00 00:00 00 does mean write out zero blocks. I know I explicitly wrote code into a revision, at a time beyond the original release of pldd, to discard writes of zero bytes quietly, rather than passing them thru to the device. I know such pass thru's trip over such unit attentions as x 6 29 reset. Pat LaVarre