From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx2.fusionio.com ([66.114.96.31]:52451 "EHLO mx2.fusionio.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755367Ab2FYPVp (ORCPT ); Mon, 25 Jun 2012 11:21:45 -0400 Date: Mon, 25 Jun 2012 11:21:42 -0400 From: Chris Mason To: "H. Peter Anvin" CC: "Chris L. Mason" , Marios Titas , linux-btrfs Subject: Re: Feature request: true RAID-1 mode Message-ID: <20120625152142.GD17638@shiny> References: <4FE1F9E4.5090301@zytor.com> <20120621005048.GA19507@shiny> <670f2f56-9918-4463-ad89-780ba80bfecc@email.android.com> MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" In-Reply-To: <670f2f56-9918-4463-ad89-780ba80bfecc@email.android.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: Yes and no. If you have 2 drives and you add one more, we can make it do all new chunks over 3 drives. But, turning the existing double mirror chunks into a triple mirror requires a balance. -chris On Wed, Jun 20, 2012 at 07:34:27PM -0600, H. Peter Anvin wrote: > Could you have a mode, though, where M = N at all times, so a user doesn't end up adding a new drive and get a nasty surprise? > > Chris Mason wrote: > > >On Wed, Jun 20, 2012 at 06:35:30PM -0600, Marios Titas wrote: > >> On Wed, Jun 20, 2012 at 12:27 PM, H. Peter Anvin > >wrote: > >> > Yet another boot loader support request. > >> > > >> > Right now btrfs' definition of "RAID-1" with more than two devices > >is a > >> > bit unorthodox: it stores on any two drives.  "True RAID-1" would > >> > instead store N copies on each of N devices, the same way an actual > >> > RAID-1 would operate with an arbitrary number of devices. > >> > > >> > This means that a bootloader can consider a single device in > >isolation: > >> > if the firmware gives access only to a single device, it can be > >booted. > >> >  Since /boot is usually a very small amount of data, this is a very > >> > reasonable tradeoff. > >> > >> +1 > >> > >> In fact, the current RAID-1 should not have been called RAID-1 at > >all, > >> it is confusing. > > > >With the raid5/6 code, I'm changing raid1 (and raid10) to have a > >configurable number of copies. So, you'll be able to have N copies on > >M > >drives, where N <= M. > > > >-chris > > -- > Sent from my mobile phone. Please excuse brevity and lack of formatting.