From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ie0-f175.google.com ([209.85.223.175]:49226 "EHLO mail-ie0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751592AbaEPSG1 (ORCPT ); Fri, 16 May 2014 14:06:27 -0400 Received: by mail-ie0-f175.google.com with SMTP id y20so2849159ier.20 for ; Fri, 16 May 2014 11:06:27 -0700 (PDT) Message-ID: <1400263584.979.17.camel@sasami.ottawa.blindsidenetworks.com> Subject: Re: RAID-1 - suboptimal write performance? From: Calvin Walton To: Tomasz Chmielewski Cc: "linux-btrfs@vger.kernel.org" Date: Fri, 16 May 2014 14:06:24 -0400 In-Reply-To: <20140516164815.1c33149b@s9> References: <20140516164815.1c33149b@s9> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Sender: linux-btrfs-owner@vger.kernel.org List-ID: On Fri, 2014-05-16 at 16:48 +0100, Tomasz Chmielewski wrote: > While doing rsyncs of large archives from one RAID-1 btrfs filesystem > to another RAID-1 btrfs filesystem: > > btrfs filesystem 1: sda + sdb (RAID-1), being copied to: > btrfs filesystem 2: sdc + sdd (RAID-1) > Server has 32 GB RAM > > > I can observe the following: > > > From time to time, rsync "freezes", while there is high IO on only *one* > of write drives. No comment on the performance issue, other than to say that I've seen similar on RAID-10 before, I think. > Also, what happens when the system crashes, and one drive has several > hundred megabytes data more than the other one? This shouldn't be an issue as long as you occasionally run a scrub or balance. The scrub should find it and fix the missing data, and a balance would just rewrite it as proper RAID-1 as a matter of course. -- Calvin Walton