From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Bryn M. Reeves" Subject: Re: dummy scsi read or scsi command periodically for external USB Hard Disk Date: Mon, 7 Jul 2014 17:25:54 +0100 Message-ID: <20140707162554.GF19630@localhost.localdomain> References: <20140707092029.GA19630@localhost.localdomain> <53BAB5DF.5090606@gmail.com> <063D6719AE5E284EB5DD2968C1650D6D1726D887@AcuExch.aculab.com> <20140707155233.GD19630@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-usb-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: loody Cc: David Laight , Lars Melin , "linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , SCSI development list List-Id: linux-scsi@vger.kernel.org On Tue, Jul 08, 2014 at 12:15:54AM +0800, loody wrote: > so sg_read will not hammer on the page cache like dd without "iflags=direct" > > thanks for your kind help, The sg_read program (and other programs in sg3_utils) sends a command directly to the device using an SG_IO ioctl. This bypasses all the caching layers in the kernel and always results in IO to the device (if it succeeds). Regards, Bryn. -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html