From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vojtech Pavlik Subject: Re: 84% -> 60% cache hit ratio for same workflow, different conf Date: Mon, 28 Mar 2016 21:17:23 +0200 Message-ID: <20160328191723.GA15859@suse.cz> References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Received: from jablonecka.jablonka.cz ([91.219.244.36]:40239 "EHLO jablonecka.jablonka.cz" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753567AbcC1TrH (ORCPT ); Mon, 28 Mar 2016 15:47:07 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-bcache-owner@vger.kernel.org List-Id: linux-bcache@vger.kernel.org To: Pradeep Jindal Cc: linux-bcache@vger.kernel.org On Mon, Mar 28, 2016 at 11:47:08PM +0530, Pradeep Jindal wrote: > Hi, > > I am facing a weird problem, I earlier had a configuration wherein my > backing device was a logical volume (LVM) backed by 3 software RAID0 > arrays having 2x1TB disks each, so totally 6TB of storage for backing > device and 300GB logical volume (LVM) backed by SSD as a caching > device. Both were configured as a cache set and I was getting around > 84% cache hit ratio. > > Now, I have changed the backing device to a bare (no LVM, no raid) 6TB > disk while everything else stays same (caching device on LVM, 300GB) > and for exactly same workload I am only getting 58-60% cache hit > ratio. > > I am confused, what could be the reason? Full stripe size writes are configured according to the backing device, for example. -- Vojtech Pavlik Director SuSE Labs