Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933423Ab3E2AiU (ORCPT ); Tue, 28 May 2013 20:38:20 -0400 Received: from mail-pd0-f182.google.com ([209.85.192.182]:56821 "EHLO mail-pd0-f182.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758214Ab3E2AiS (ORCPT ); Tue, 28 May 2013 20:38:18 -0400 Date: Tue, 28 May 2013 17:38:15 -0700 From: Kent Overstreet To: Duncan <1i5t5.duncan@cox.net> Cc: linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org Subject: Re: [RFC PATCH v1 0/5] BTRFS hot relocation support Message-ID: <20130529003815.GE2291@google.com> References: <1369062687-23544-1-git-send-email-zwu.kernel@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2038 Lines: 37 On Tue, May 21, 2013 at 02:22:34AM +0000, Duncan wrote: > zwu.kernel posted on Mon, 20 May 2013 23:11:22 +0800 as excerpted: > > > The patchset is trying to introduce hot relocation support > > for BTRFS. In hybrid storage environment, when the data in rotating disk > > get hot, it can be relocated to nonrotating disk by BTRFS hot relocation > > support automatically; also, if nonrotating disk ratio exceed its upper > > threshold, the data which get cold can be looked up and relocated to > > rotating disk to make more space in nonrotating disk at first, and then > > the data which get hot will be relocated to nonrotating disk > > automatically. > > One advantage of a filesystem implementation, as opposed to bcache or > dmcache, is arguably a corner-case, but it's /my/ corner-case, so... > > I run an intr*-less (I guess technically, empty initramfs) monolithic- > kernel boot, using the kernel commandline root= and (formerly) md= and > related logic to choose/assemble/mount root directly from the kernel > command line via bootloader (grub2). Thus, any user-space-required-to- > mount-root is out, since I don't have an initr* and thus no early > userspace. That means both lvm2 and dmcache (AFAIK) are out. I'm not > sure about bcache, but it has other negatives, particularly against btrfs- > raid-1 and I'd guess md/raid-1 as well. > > Much like md before it, btrfs, while normally requiring the user-space- > required device-scan to properly handle multiple devices, has kernel- > command-line options that allow direct kernel multi-device assembly > without the help of early-userspace/initr*. I wouldn't be averse to adding such functionality to bcache, provided it could be done reasonably cleanly/sensibly. It's not high on my list but I'd accept patches :) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/