linux-kernel - Re: [RFC PATCH 0/5] Btrfs: Add hot data tracking functionality

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Message-ID: <4C4F6DF2.6090905@ontolinux.com>
Date:	Wed, 28 Jul 2010 01:38:26 +0200
From:	Christian Stroetmann <stroetmann@...olinux.com>
To:	bchociej@...il.com, linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC PATCH 0/5] Btrfs: Add hot data tracking functionality

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
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