From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from [195.159.176.226] ([195.159.176.226]:60790 "EHLO blaine.gmane.org" rhost-flags-FAIL-FAIL-OK-OK) by vger.kernel.org with ESMTP id S933581AbdJREvV (ORCPT ); Wed, 18 Oct 2017 00:51:21 -0400 Received: from list by blaine.gmane.org with local (Exim 4.84_2) (envelope-from ) id 1e4gJu-0006Jr-Py for linux-btrfs@vger.kernel.org; Wed, 18 Oct 2017 06:51:06 +0200 To: linux-btrfs@vger.kernel.org From: Duncan <1i5t5.duncan@cox.net> Subject: Re: Is it safe to use btrfs on top of different types of devices? Date: Wed, 18 Oct 2017 04:50:53 +0000 (UTC) Message-ID: References: <20171017011443.bupcsskm7joc73wb@angband.pl> <81e1136a-a846-9531-b1bf-9ad2aabb785d@gmail.com> <20171017170626.amfrohfyqlujdueu@angband.pl> <1d5e9875-1c1e-f67e-1f5b-0741555d9517@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: Austin S. Hemmelgarn posted on Tue, 17 Oct 2017 15:19:09 -0400 as excerpted: >> It's a single-device filesystem, thus disconnects are obviously fatal. >> But, >> they never caused even a single bit of damage (as scrub goes), thus >> proving btrfs handles this kind of disconnects well. Unlike times >> past, the kernel doesn't get confused thus no reboot is needed, merely >> an unmount, "service nbd-client restart", mount, restart the rebuild >> jobs. > That's expected behavior though. _Single_ device BTRFS has nothing to > get out of sync most of the time, the only time there's any possibility > of an issue is when you die after writing the first copy of a block > that's in a dup profile chunk, but even that is not very likely to cause > problems (you'll just lose at most the last worth of > data). The moment you add another device though, that simplicity goes > out the window. This is why I said if you /must/ work with USB-connected devices, I'd suggest single-device btrfs, tho I'd go full dup (data too) to take advantage of the btrfs ability to detect checksum errors and rewrite a bad copy from the second, hopefully good, copy. Single device simply doesn't have the sync issues of multi-device, even in dup mode, so end up being much more reliable in cases like USB connection (and NBD as in the example above), where connection reliability is a problem. -- Duncan - List replies preferred. No HTML msgs. "Every nonfree program has a lord, a master -- and if you use the program, he is your master." Richard Stallman