From mboxrd@z Thu Jan 1 00:00:00 1970 From: Brad Campbell Subject: Re: mdadm raid1 read performance Date: Wed, 04 May 2011 14:31:18 +0800 Message-ID: <4DC0F2B6.9050708@fnarfbargle.com> References: <20110504105822.21e23bc3@notabene.brown> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Drew Cc: NeilBrown , Liam Kurmos , linux-raid@vger.kernel.org List-Id: linux-raid.ids On 04/05/11 13:30, Drew wrote: > It seemed logical to me that if two disks had the same data and we > were reading an arbitrary amount of data, why couldn't we split the > read across both disks? That way we get the benefits of pulling from > multiple disks in the read case while accepting the penalty of a write > being as slow as the slowest disk.. > > I would have thought as you'd be skipping alternate "stripes" on each disk you minimise the benefit of a readahead buffer and get subjected to seek and rotational latency on both disks. Overall you're benefit would be slim to immeasurable. Now on SSD's I could see it providing some extra oomph as you suffer none of the mechanical latency penalties.