From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christian Stroetmann Subject: Re: [RFC PATCH 0/5] Btrfs: Add hot data tracking functionality Date: Wed, 28 Jul 2010 01:38:26 +0200 Message-ID: <4C4F6DF2.6090905@ontolinux.com> References: <1280268023-18408-1-git-send-email-bchociej@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15; format=flowed Content-Transfer-Encoding: 7bit To: bchociej@gmail.com, linux-kernel , linux-fsdevel Return-path: In-Reply-To: <1280268023-18408-1-git-send-email-bchociej@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org At the 28.07.2010 00:00, Ben Chociej wrote: > INTRODUCTION: > > This patch series adds experimental support for tracking data > temperature in Btrfs. Essentially, this means maintaining some key > stats (like number of reads/writes, last read/write time, frequency of > reads/writes), then distilling those numbers down to a single > "temperature" value that reflects what data is "hot." > > The long-term goal of these patches, as discussed in the Motivation > section at the end of this message, is to enable Btrfs to perform > automagic relocation of hot data to fast media like SSD. This goal has > been motivated by the Project Ideas page on the Btrfs wiki. > > Of course, users are warned not to run this code outside of development > environments. These patches are EXPERIMENTAL, and as such they might > eat your data and/or memory. > > > MOTIVATION: > > The overall goal of enabling hot data relocation to SSD has been > motivated by the Project Ideas page on the Btrfs wiki at > https://btrfs.wiki.kernel.org/index.php/Project_ideas. It is hoped that > this initial patchset will eventually mature into a usable hybrid > storage feature set for Btrfs. > > This is essentially the traditional cache argument: SSD is fast and > expensive; HDD is cheap but slow. ZFS, for example, can already take > advantage of SSD caching. Btrfs should also be able to take advantage > of hybrid storage without any broad, sweeping changes to existing code. > Wouldn't this feature be useful for other file systems as well, so that a more general and not an only Btrfs related solution is preferable? > With Btrfs's COW approach, an external cache (where data is *moved* to > SSD, rather than just cached there) makes a lot of sense. Though these > patches don't enable any relocation yet, they do lay an essential > foundation for enabling that functionality in the near future. We plan > to roll out an additional patchset introducing some of the automatic > migration functionality in the next few weeks. > > With all the best Christian Stroetmann