From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from p3nlsmtpcp01-02.prod.phx3.secureserver.net ([184.168.200.140]:36918 "EHLO p3nlsmtpcp01-02.prod.phx3.secureserver.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751516AbdBUKPO (ORCPT ); Tue, 21 Feb 2017 05:15:14 -0500 Date: Tue, 21 Feb 2017 15:44:01 +0530 From: "Lakshmipathi.G" To: Qu Wenruo Cc: linux-btrfs@vger.kernel.org Subject: Re: Large no.of extents for a single small file with a fresh RAID5 setup Message-ID: <20170221101401.GA5498@giis.co.in> References: <20170218020711.GA23608@giis.co.in> <678a9608-8f42-119c-7fd3-69fbae31bfab@cn.fujitsu.com> <20170220140737.GA27535@giis.co.in> <20170221092215.GA5217@giis.co.in> <1b567b5e-8035-33ce-ddd2-2e19065044c6@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii In-Reply-To: <1b567b5e-8035-33ce-ddd2-2e19065044c6@cn.fujitsu.com> Sender: linux-btrfs-owner@vger.kernel.org List-ID: > > >I'm using Ubuntu(16.04) desktop version (not server) running Xorg and others. May be its possible its > >flushing data to disk at constant time. If you like to give it a try again with servers, below is the > >exact script along with its timing & multiextent output. > > Archlinux here, with my btrfs vm and browser and music player, still one > extent. > looks like I have better setup to produce single-extent files than yours :-) > Are you under heavy memory usage? > no, not as per top and free. 'top' shows mem.usage as: KiB Mem : 7092516 total, 5961796 free, 794836 used, 335884 buff/cache where 'compiz' process uses around 2.5% of memory and 'free' command reports almost 5gb as free. May be some 'sysctl' or others needs to be adjusted on my setup? > > > >one more curious thing, is it fine to have extents with size 4096 on RAID5 setup? > > > > Sure, why not? > > Any size aligned to sector size is valid, no matter the profile. > > For 4K extent, RAID5/6 will do read-modify-write, which is very common. > > Thanks, > Qu > While looking into mapping from logical->physical chunks on RAID5. I was wondering how these 4KB extents will fit into 64KB data-stripe? I didn't have idea about read-modify-write, just found few wiki links on it, will check. thanks Cheers. Lakshmipathi.G