From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f51.google.com ([209.85.218.51]:36703 "EHLO mail-oi0-f51.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932581AbaICPpm (ORCPT ); Wed, 3 Sep 2014 11:45:42 -0400 Received: by mail-oi0-f51.google.com with SMTP id v63so5730865oia.10 for ; Wed, 03 Sep 2014 08:45:41 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: <9437B859-6FD7-4971-935A-E29EFBB7B261@colorremedies.com> References: <20140812011401.568c16e6@natsu> <9EB33BE3-FAC0-4AE8-BB95-ABE68C578D47@colorremedies.com> <08770CD2-AA55-4BC1-B92C-E7D3360399F8@colorremedies.com> <5CE63712-2C3E-4BF3-B971-C6F17AE10E3D@colorremedies.com> <540617DE.5070605@gmail.com> <88B7E732-0EB2-422C-B5C7-950E483C2E71@colorremedies.com> <9437B859-6FD7-4971-935A-E29EFBB7B261@colorremedies.com> Date: Wed, 3 Sep 2014 08:45:40 -0700 Message-ID: Subject: Re: Large files, nodatacow and fragmentation From: "G. Richard Bellamy" To: Chris Murphy Cc: linux-btrfs Content-Type: text/plain; charset=UTF-8 Sender: linux-btrfs-owner@vger.kernel.org List-ID: It is interesting that for me the number of extents before and after bcache are essentially the same. The lesson here for me there is that the fragmentation of a btrfs nodatacow file is not mitigated by bcache. There seems to be nothing I can do to prevent that fragmentation, and may in fact be expected behavior. I cannot prove that adding the SSD bcache front-end improved performance of the guest VM, though subjectively it seems to have had a positive effect. There is something systemically pathological with the VM in question, but that's a different mailing list. :) -rb On Tue, Sep 2, 2014 at 11:26 PM, Chris Murphy wrote: > > On Sep 3, 2014, at 12:01 AM, Chris Murphy wrote: > >> I created two pools, one xfs one btrfs, default formatting and mount options. I then created a qcow2 file on each using virt-manager, also using default options. And default caching (whatever that is, I think it's writethrough but don't hold me to it). > > On the btrfs qcow2, xattr C was set. > > > Chris Murphy-- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html