From mboxrd@z Thu Jan 1 00:00:00 1970 From: keld@keldix.com Subject: Re: Why are reads not balanced across my RAID-1? Date: Fri, 24 Jan 2014 18:49:04 +0100 Message-ID: <20140124174904.GA6884@www5.open-std.org> References: <20140124104757.8256.qmail@science.horizon.com> <20140124120448.GA19163@www5.open-std.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Matt Garman Cc: George Spelvin , Mdadm List-Id: linux-raid.ids On Fri, Jan 24, 2014 at 08:56:02AM -0600, Matt Garman wrote: > On Fri, Jan 24, 2014 at 6:04 AM, wrote: > > The reading is not balanced because it does not make sense to do balanced > > reads for sequential reading. In RAID-1 the disk sectors are consequitive. > > So if you would read one sector from one disk, and the following sector from the other disk, > > then the next read from disk 1 would need to skip a full resolvation of the disk, > > which may cost something like 8 ms. So better read contigously from the same disk, and hope > > for some other IO request that can use disk 2. > > > Does that rationale hold for SSDs? No, this is not relevant for SSDs as access time is almost zero. best regards keld