From mboxrd@z Thu Jan 1 00:00:00 1970 From: The Ghost Subject: Does ext4 write anything during reading with relatime? Date: Sat, 05 Dec 2015 14:03:14 +0300 Message-ID: <5662C472.2050902@inbox.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit To: linux-ext4@vger.kernel.org Return-path: Received: from fallback6.mail.ru ([94.100.181.147]:54717 "EHLO fallback6.mail.ru" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753584AbbLELFQ (ORCPT ); Sat, 5 Dec 2015 06:05:16 -0500 Received: from smtp32.i.mail.ru (smtp32.i.mail.ru [94.100.177.92]) by fallback6.mail.ru (mPOP.Fallback_MX) with ESMTP id 89356193DC85 for ; Sat, 5 Dec 2015 14:03:19 +0300 (MSK) Received: from ip-95-220-88-90.bb.netbynet.ru ([95.220.88.90]:39636 helo=[192.168.1.9]) by smtp32.i.mail.ru with esmtpa (envelope-from ) id 1a5AcX-00089v-2J for linux-ext4@vger.kernel.org; Sat, 05 Dec 2015 14:03:17 +0300 Sender: linux-ext4-owner@vger.kernel.org List-ID: When mounted read-only, naturally, reading from an ext4 filesystem does not cause any write operations. But if I mount it read-write and try to read from it, then apparently some write operations are issued, because my "write-mostly" drive in a RAID1 array spins up. Now, I understand that apparently the mount operation itself does write something, and I do mount it with a "relatime" option, but I'm just reading stuff over and over again - it shouldn't be caused by atime updating. Also, a bug with "write-mostly" finally got fixed, and I'm using a fixed kernel (latest 3.16 from Debian Jessie-backports). I just want someone to explain what's happening or direct me towards some information about that, because I just want to understand. :) And I don't know any means to find out myself... if there are any, those would require much better understanding of filesystems than I have... -- The Ghost