From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from drax.kayaks.hungrycats.org (drax.kayaks.hungrycats.org [174.142.148.226]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C2D4719F119 for ; Tue, 10 Dec 2024 02:42:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=174.142.148.226 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733798535; cv=none; b=UfGzd2H6Dcr40Y0G1P5rRR4STkRHC/arNmiYA24z/5aiRTPsrWLQqzY7wuWyJGshhhomLMdWyNCJtxax2jWofW34wva7CWfN2jOMdyT9Kvyy+N3Zc5uG8IQ+nKaK1bhmw8IxqrUAf0KHvhkKUJqn6kSfk8i3WMGm8ms8qjsdTGM= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1733798535; c=relaxed/simple; bh=tBoHU33q/hm2627qob5zROkByzdgBjcBjbjcjKP3N5c=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=Ro+s6O2BwvMoOm36m9xbPJgeJbM8Nqzwrb1LX8K7OJvMLq0do4YV8RQrjSTtHvvXSCm//yFtb/TFXHf/pIDZBfppmoeswk/JLEUX1mThn6YYNOLlwi8NoE7myx8pizan71GO4CxL8br03y3n01hwYMg0w+9lj1bY1Li+Rczrlss= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=umail.furryterror.org; spf=pass smtp.mailfrom=drax.hungrycats.org; arc=none smtp.client-ip=174.142.148.226 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=umail.furryterror.org Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=drax.hungrycats.org Received: by drax.kayaks.hungrycats.org (Postfix, from userid 1002) id 30BED1128BF6; Mon, 9 Dec 2024 21:42:13 -0500 (EST) Date: Mon, 9 Dec 2024 21:42:13 -0500 From: Zygo Blaxell To: Scoopta Cc: linux-btrfs@vger.kernel.org Subject: Re: Safety of raid1 vs raid10 Message-ID: References: Precedence: bulk X-Mailing-List: linux-btrfs@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Mon, Dec 09, 2024 at 06:26:24PM -0800, Scoopta wrote: > I've read online that btrfs raid10 is theoretically safer than raid1 because > raid10 groups drives together into mirrored pairs making the filesystem more > likely to successfully survive a multi-drive failure event. I can't find any > documentation that says this to be the case. Is it true that btrfs pairs > drives together for raid10 but not raid1, if this is the case what's the > reasoning for it? It is _possible_ for raid10 and raid1 to be arranged such that multiple drive losses are possible. e.g. if all odd numbered devices are paired with all even numbered devices, then any odd numbered device can be lost and the filesystem still survives. This is not _guaranteed_, it is only _possible_. In a filesystem with an odd number of drives, or with drives of varying sizes, the block groups will only guarantee that one drive loss can be tolerated in each block group, in order to have the flexibility needed to fill all available space. In such cases it is common that block groups are arranged in such a way that loss of any two drives will break the filesystem.