From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx3.redhat.com (mx3.redhat.com [172.16.48.32]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id n2GEaWM7016367 for ; Mon, 16 Mar 2009 10:36:32 -0400 Received: from nazgul.esiway.net (Nazgul.ESIWAY.NET [193.194.16.154]) by mx3.redhat.com (8.13.8/8.13.8) with ESMTP id n2GEaKGt003407 for ; Mon, 16 Mar 2009 10:36:21 -0400 Received: from Megathlon.ESI (Ghost.esi.it [193.194.16.225]) by nazgul.esiway.net (8.13.8/8.13.8) with ESMTPS id n2GEaJs8011319 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=OK) for ; Mon, 16 Mar 2009 15:36:19 +0100 Received: from frodo.esi (Frodo.ESI [10.10.10.13]) by Megathlon.ESI (8.14.1/8.14.1) with ESMTP id n2GEaIH6021920 for ; Mon, 16 Mar 2009 15:36:19 +0100 Message-ID: <49BE63E2.5010001@esiway.net> Date: Mon, 16 Mar 2009 15:36:18 +0100 From: Marco Colombo MIME-Version: 1.0 Subject: Re: [linux-lvm] fsync() and LVM References: <49BA9BF9.3070507@esiway.net> <20090313203812.GK7445@agk.fab.redhat.com> <7B7881568CF40E4388B615CD06F87B98098BDA@clara.maurer-it.com> <49BC511E.5040402@esiway.net> <49BE31CC.7050905@Media-Brokers.com> In-Reply-To: <49BE31CC.7050905@Media-Brokers.com> Content-Transfer-Encoding: 7bit Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii" To: LVM general discussion and development Charles Marcus wrote: > On 3/14/2009 8:51 PM, Marco Colombo wrote: >> Stuart D. Gathman wrote: >>> On Sat, 14 Mar 2009, Dietmar Maurer wrote: >>> It just means that write barriers won't get passed to the device. >>> This is only a problem if the devices have write caches. Note >>> that with multiple devices, even a FIFO write cache could cause >>> reordering between devices (one device could finish faster than another). > >> No, it's more than that. PostgreSQL gurus say LVM doesn't honor fsync(), >> that data doesn't even get to the controller, and it doesn't matter >> if the disks have write caches enabled or not. Or if they have battery backed >> caches. Please read the thread I linked. If what they say it's true, >> you can't use LVM for anything that needs fsync(), including mail queues >> (sendmail), mail storage (imapd), as such. So I'd really like to know. > > Seeing as my /var (with both postfix & courier-imap using it for mail > storage) has been on lvm for almost 4 years, that would be news to me... > > ;) > Believe me or not, they both depend on fsync(). Anyway, even if you lost a message, how do you expect to know? If you have any user base large enough, you're used to 'missing' messages (99% of the user-deleted or user-never-sent kind). A truly lost one may have gone missed in the noise. A lying fsync() doesn't blow all your mail repository up, just you may loose one/two messages on a crash. Or a transaction, speaking of databases. If that's the case, I would like to know, that's all. .TM.