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[70.62.41.24]) by smtp.gmail.com with ESMTPSA id j5sm9031104ita.16.2019.04.29.04.43.10 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Mon, 29 Apr 2019 04:43:11 -0700 (PDT) Subject: Re: Migration to BTRFS To: Andrei Borzenkov , Hendrik Friedel , "linux-btrfs@vger.kernel.org" References: <0f1a1f40-c951-05dc-f9fd-d6de5884f782@gmail.com> From: "Austin S. Hemmelgarn" Message-ID: Date: Mon, 29 Apr 2019 07:43:08 -0400 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <0f1a1f40-c951-05dc-f9fd-d6de5884f782@gmail.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 2019-04-28 16:14, Andrei Borzenkov wrote: > 28.04.2019 22:35, Hendrik Friedel пишет: >> Hello, >> >> I intend to move to BTRFS and of course I have some data already. >> I currently have several single 4TB drives and I would like to move the >> Data onto new drives (2*8TB). I need no raid, as I prefer a backup. >> Nevertheless, having raid nice for availability. So why not in the end. >> I currently use ~6TB, so it may work, but I would be able to remove the >> redundancy later. >> >> So, if I understand correctly, today I want >> -m raid1 -d raid1 >> >> whereas later, I want >> -m raid1 -d single >> >> What is very important to me is, that with one failing drive, I have no >> risk of losing the whole filesystem, but only losing the affected drive. >> Is that possible with both of these variants? >> > > With "single" data profile you won't lose filesystem, but you will > irretrievably lose any data on the missing drive. Also "single" profile > does not support auto-healing (repairing of bad copy from good copy). If > this is acceptable to you, then yes, both variants will do what you want. Actually, it's a bit worse than this potentially. You may lose individual files if you lose one disk with the proposed setup, but you may also lose _parts_ of individual files, especially if you have lots of large (>1-5GB in size) files. And on top of this, finding what data went missing will essentially require trying to read every byte of every file in the volume. > >> Is it possible to move between the two (doing a balance, of course? > > Yes as long as you have sufficient free space for target profile. > >> Any other thoughts/recommendations? >> > > As of today there is no provision for automatic mounting of incomplete > multi-device btrfs in degraded mode. Actually, with systemd it is flat > impossible to mount incomplete btrfs because standard framework only > proceeds to mount it after all devices have been seen. As long as you do > not use systemd in initramfs you may be able to boot by passing suitable > root mount flags on kernel command line. >