Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756023Ab0HaWBQ (ORCPT ); Tue, 31 Aug 2010 18:01:16 -0400 Received: from m209-5.dsl.rawbw.com ([198.144.209.5]:50714 "EHLO kyoto.noir.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751700Ab0HaWBP (ORCPT ); Tue, 31 Aug 2010 18:01:15 -0400 Message-ID: <4C7D7BA5.6080607@noir.com> Date: Tue, 31 Aug 2010 15:01:09 -0700 From: "K. Richard Pixley" User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.6; en-US; rv:1.9.2.8) Gecko/20100802 Lightning/1.0b2 Thunderbird/3.1.2 MIME-Version: 1.0 To: Mike Fedyk CC: Josef Bacik , Tomasz Chmielewski , linux-kernel@vger.kernel.org, linux-btrfs@vger.kernel.org, hch@infradead.org, gg.mariotti@gmail.com, "Justin P. Mattock" , mjt@tls.msk.ru, tytso@mit.edu Subject: Re: BTRFS: Unbelievably slow with kvm/qemu References: <4C7AB645.5090804@wpkg.org> <20100830001441.GA838@dhcp231-156.rdu.redhat.com> <4C7BD569.9000702@noir.com> In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1664 Lines: 35 On 20100831 14:46, Mike Fedyk wrote: > There is little reason not to use duplicate metadata. Only small > files (less than 2kb) get stored in the tree, so there should be no > worries about images being duplicated without data duplication set at > mkfs time. My benchmarks show that for my kinds of data, btrfs is somewhat slower than ext4, (which is slightly slower than ext3 which is somewhat slower than ext2), when using the defaults, (ie, duplicate metadata). It's a hair faster than ext2, (the fastest of the ext family), when using singleton metadata. And ext2 isn't even crash resistant while btrfs has snapshots. I'm using hardware raid for striping speed. (Tried btrfs striping, it was close, but not as fast on my hardware). I want speed, speed, speed. My data is only vaguely important, (continuous builders), but speed is everything. While the reason to use singleton metadata may be "little", it dominates my application. If I were forced to use duplicate metadata then I'd still be arguing with my coworkers about whether the speed costs were worth it to buy snapshot functionality. But the fact that btrfs is faster AND provides snapshots, (and less metadata overhead and bigger file systems and etc), makes for an easy sale. Note that nilfs2 has similar performance, but somewhat different snapshot characteristics that aren't as useful in my current application. --rich -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/