From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: linux-nfs-owner@vger.kernel.org Received: from smtp-outbound-1.vmware.com ([208.91.2.12]:37076 "EHLO smtp-outbound-1.vmware.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754463Ab2CPSOF (ORCPT ); Fri, 16 Mar 2012 14:14:05 -0400 Received: from sc9-mailhost2.vmware.com (sc9-mailhost2.vmware.com [10.113.161.72]) by smtp-outbound-1.vmware.com (Postfix) with ESMTP id 27C9728206 for ; Fri, 16 Mar 2012 11:14:04 -0700 (PDT) Received: from zimbra-prod-mta-3.vmware.com (zimbra-prod-mta-3.vmware.com [10.113.160.227]) by sc9-mailhost2.vmware.com (Postfix) with ESMTP id 22EE0B03FB for ; Fri, 16 Mar 2012 11:14:04 -0700 (PDT) Received: from localhost (localhost.localdomain [127.0.0.1]) by zimbra-prod-mta-3.vmware.com (Postfix) with ESMTP id 1D61B100712 for ; Fri, 16 Mar 2012 11:14:04 -0700 (PDT) Received: from zimbra-prod-mta-3.vmware.com ([127.0.0.1]) by localhost (zimbra-prod-mta-3.vmware.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id hOgrd3+dEgLD for ; Fri, 16 Mar 2012 11:14:04 -0700 (PDT) Received: from zimbra-prod-mbox-3.vmware.com (zimbra-prod-mbox-3.vmware.com [10.113.160.203]) by zimbra-prod-mta-3.vmware.com (Postfix) with ESMTP id 0A14E1006EC for ; Fri, 16 Mar 2012 11:14:04 -0700 (PDT) From: "Alexandre Depoutovitch" To: References: In-Reply-To: Subject: About Direct I/O Date: Fri, 16 Mar 2012 11:14:04 -0700 (PDT) Message-ID: <6866525b.00001bd8.0000023d@aldep-VC.vmware.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Sender: linux-nfs-owner@vger.kernel.org List-ID: Hello, I am trying to do random sector aligned writes to an NFS mounted disk. The performance is order of magnitude worse than 4K (file system block size) aligned I/O. The reason is that NFS demon (Linux kernel 2.6.32) on the server side always does buffered I/O, which behaves poorly for block unaligned requests. Is there a way to tell NFS daemon to use direct I/O? If not, is it an implementation limitation or there is a fundamental problem with using direct I/O in NFS server? Thank you, Alex