From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from plane.gmane.org ([80.91.229.3]:54779 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932305AbaH0WFG (ORCPT ); Wed, 27 Aug 2014 18:05:06 -0400 Received: from list by plane.gmane.org with local (Exim 4.69) (envelope-from ) id 1XMlKx-0007ao-BE for linux-btrfs@vger.kernel.org; Thu, 28 Aug 2014 00:05:03 +0200 Received: from cable-192.222.157.175.electronicbox.net ([192.222.157.175]) by main.gmane.org with esmtp (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 28 Aug 2014 00:05:03 +0200 Received: from ngrigoriev by cable-192.222.157.175.electronicbox.net with local (Gmexim 0.1 (Debian)) id 1AlnuQ-0007hv-00 for ; Thu, 28 Aug 2014 00:05:03 +0200 To: linux-btrfs@vger.kernel.org From: Nikolai Grigoriev Subject: Re: ext4 vs btrfs performance on SSD array Date: Wed, 27 Aug 2014 21:59:50 +0000 (UTC) Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-btrfs-owner@vger.kernel.org List-ID: Duncan <1i5t5.duncan cox.net> writes: > > Nikolai Grigoriev posted on Tue, 26 Aug 2014 19:39:08 -0400 as excerpted: > > > Kernel: 3.8.13-35.3.5.el6uek.x86_64 #2 SMP Fri Aug 8 21:58:11 PDT 2014 > > x86_64 x86_64 x86_64 GNU/Linux > > > Btrfs v0.20-rc1 > > I've no answer for your question, but you know how old both your kernel > and btrfs-progs versions are, for a filesystem under as heavy development > as btrfs is, right? Yes. As much as I'd like to run latest & greatest the company sticks to OEL 6.5 so I have to play within the limits. The primary reason why I asked the question is because I have noticed that "btrfs does it much better :)" and wanted to understand why. Either to understand ext4 limitations vs btrfs or to understand the issues with my ext4 configuration. Actually, I have found the answer later last night. I have found that btrfs has its own readahead implementation. So I've got an idea to disable it and see if it makes it slower. And, indeed, I can confirm that in my specific test scenario the readahead with 4Mb (default) buffer was making lots of difference. I think it was mostly due to RAID-0 with 2 SSDs. But even on a single filesystem it does make a difference. Then I have also realized that since it was due to readahead, it won't be a big game changer for Cassandra as it does lots of random reads. But thanks anyway for the detailed explanation of BTRFS status. I'll surely use it as soon as I can.