From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bernd Schubert Subject: Re: md question re: max_hw_sectors_kb Date: Wed, 04 May 2011 20:08:02 +0200 Message-ID: <4DC19602.9060401@itwm.fraunhofer.de> References: <4DC0639E.1070707@sgi.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: "Martin K. Petersen" Cc: Michael Reed , linux-raid@vger.kernel.org, neilb@suse.de, Jeremy Higdon , Hannes Reinecke List-Id: linux-raid.ids On 05/04/2011 07:58 PM, Martin K. Petersen wrote: >>>>>> "Michael" == Michael Reed writes: > > Michael> There is code in blk_queue_make_request() which lowers the > Michael> default value from INT_MAX to BLK_SAFE_MAX_SECTORS, which is > Michael> 255. This is generally lower than all the underlying devices > Michael> with which I use md. > > Yeah, the SAFE value is there to appease legacy low-level drivers. > > > Michael> As md appears to be a stacking driver, i.e., it calls > Michael> disk_stack_limits() for each member of a volume, it would seem > Michael> reasonable for md to use the, INT_MAX setting for > Michael> max_hw_sectors_kb instead of BLK_SAFE_MAX_SECTORS. > > Your fix is functionally correct. However, another case just popped up > this week where we need to distinguish between stacking driver and LLD > defaults. So I think we should try to handle this at the block layer > instead of explicitly tweaking this knob in MD. > > I'll get this fixed up and will CC: you on the patch. > Could you please CC me or linux-raid as well? I have a similar patch for raid1 and while I'm not working on Lustre anymore, I know that Lustre also always has a another kernel patch for raid5... Thanks, Bernd