From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from rin.romanrm.net ([91.121.86.59]:44256 "EHLO rin.romanrm.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750703AbeCJSba (ORCPT ); Sat, 10 Mar 2018 13:31:30 -0500 Date: Sat, 10 Mar 2018 23:31:27 +0500 From: Roman Mamedov To: Adam Borowski Cc: Christoph Anton Mitterer , "linux-btrfs@vger.kernel.org" Subject: Re: zerofree btrfs support? Message-ID: <20180310233127.0dfa7823@natsu> In-Reply-To: <20180310155022.wtdmwiyxu7mxt74s@angband.pl> References: <1520650525.5641.47.camel@scientia.net> <20180310081606.7c2u2dtopijujhbz@angband.pl> <1520691545.24363.10.camel@scientia.net> <20180310193722.2d6b494a@natsu> <20180310155022.wtdmwiyxu7mxt74s@angband.pl> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Sat, 10 Mar 2018 16:50:22 +0100 Adam Borowski wrote: > Since we're on a btrfs mailing list, if you use qemu, you really want > sparse format:raw instead of qcow2 or preallocated raw. This also works > great with TRIM. Agreed, that's why I use RAW. QCOW2 would add a second layer of COW on top of Btrfs, which sounds like a nightmare. Even if you would run those files as NOCOW in Btrfs, somehow I feel FS-native COW is more efficient than emulating it in userspace with special format files. > > It works, just not with some of the QEMU virtualized disk device drivers. > > You don't need to use qemu-img to manually dig holes either, it's all > > automatic. > > It works only with scsi and virtio-scsi drivers. Most qemu setups use > either ide (ouch!) or virtio-blk. It works with IDE as well. -- With respect, Roman