From mboxrd@z Thu Jan 1 00:00:00 1970 From: Laurence Oberman Subject: Re: All scsi_debug devices in the scsi_debug driver share the same RAM space Date: Mon, 05 Feb 2018 09:32:31 -0500 Message-ID: <1517841151.11655.1.camel@redhat.com> References: <1517686992.18584.8.camel@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: Received: from mail-qk0-f180.google.com ([209.85.220.180]:34799 "EHLO mail-qk0-f180.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752612AbeBEOcd (ORCPT ); Mon, 5 Feb 2018 09:32:33 -0500 Received: by mail-qk0-f180.google.com with SMTP id m130so7790902qke.1 for ; Mon, 05 Feb 2018 06:32:33 -0800 (PST) In-Reply-To: <1517686992.18584.8.camel@redhat.com> Sender: linux-scsi-owner@vger.kernel.org List-Id: linux-scsi@vger.kernel.org To: dgilbert , linux-scsi@vger.kernel.org, Bart Van Assche Cc: John Pittman , Jon Magrini On Sat, 2018-02-03 at 14:43 -0500, Laurence Oberman wrote: > Hello Doug > > I had emailed you earlier about this issue forgetting to copy others. > > All test devices in the scsi_debug driver share the same ram space so > we cannot really have individual devices for testing stuff like md- > raid. > > I bumped into this a few times already and I think it would be useful > to make each device an individual RAM entry so we can create multiple > unique devices. > > Of course this means also now having to maybe start using attributes > for each device do we can selectively choose which devices get the > fault injections. > > I know its adding complexity here but wanted to get input about the > possibility of changing this. > > For a particular fault injection case this morning I had to use 5 > regular drives and 1 scsi-debug drive to inject faults to reproduce > an > md-raid issue. > > I also wanted a different start sector and range and sent an earlier > patch for that. > > So is this something worth considering ? > If so, i will start working on it. > > Regards > Laurence > > > > I chatted with Doug about this. Seems that many of the use cases for scsi_debug involved creating high count devices for testing etc. so having each with its own ram space could land up chewing a bunch of memory. I am going to drop this idea for now, but the patch I sent for the choice of sector for MEDIUM errors and count is very useful so I hope that one gets accepted. That patch changes nothing if the two new parameters are not set so should be low risk for acceptance. Thanks Laurence