From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from lb1.pop2.wanet.net ([65.244.248.2]:59318 "EHLO serv004.pop2.wanet.net" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751425AbaL3XRT (ORCPT ); Tue, 30 Dec 2014 18:17:19 -0500 Message-ID: <40b56c60ddd4801295a92c4b11d5c08e.squirrel@webmail.wanet.net> In-Reply-To: <54A31CAE.4020606@ubuntu.com> References: <7e0d08fddb1e0060f756690f6c82c350.squirrel@webmail.wanet.net> <54A31CAE.4020606@ubuntu.com> Date: Tue, 30 Dec 2014 15:17:17 -0800 Subject: Re: I need to P. are we almost there yet? From: ashford@whisperpc.com To: "Phillip Susi" , "Jose Manuel Perez Bethencourt" Cc: ashford@whisperpc.com, "Chris Murphy" , "sys.syphus" , "Btrfs BTRFS" MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-btrfs-owner@vger.kernel.org List-ID: > Phillip Susi wrote: > >> I'm wondering which of the above the BTRFS implementation most >> closely resembles. > > Unfortunately, btrfs just uses the naive raid1+0, so no 2 or 3 disk > raid10 arrays, and no higher performing offset layout. > Jose Manuel Perez Bethencourt wrote: > > I think you are missing crucial info on the layout on disk that BTRFS > implements. While a traditional RAID1 has a rigid layout that has > fixed and easily predictable locations for all data (exactly on two > specific disks), BTRFS allocs chunks as needed on ANY two disks. > Please research into this to understand the problem fully, this is the > key to your question. There is a HUGE difference here. In the first case, the data will have a >50% chance of surviving a 2-drive failure. In the second case, the data will have an effectively 0% chance of surviving a 2-drive failure. I don't believe I need to mention which of the above is more reliable, or which I would prefer. I believe that someone who understands the code in depth (and that may also be one of the people above) determine exactly how BTRFS implements RAID-10. Thank you. Peter Ashford