From owner-freebsd-fs@FreeBSD.ORG Wed Sep 22 17:19:24 2010 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id C81611065670 for ; Wed, 22 Sep 2010 17:19:24 +0000 (UTC) (envelope-from gull@gull.us) Received: from mail-ey0-f182.google.com (mail-ey0-f182.google.com [209.85.215.182]) by mx1.freebsd.org (Postfix) with ESMTP id 62D268FC12 for ; Wed, 22 Sep 2010 17:19:23 +0000 (UTC) Received: by eyx24 with SMTP id 24so262286eyx.13 for ; Wed, 22 Sep 2010 10:19:23 -0700 (PDT) MIME-Version: 1.0 Received: by 10.213.4.73 with SMTP id 9mr1077037ebq.5.1285175963158; Wed, 22 Sep 2010 10:19:23 -0700 (PDT) Received: by 10.14.29.76 with HTTP; Wed, 22 Sep 2010 10:19:22 -0700 (PDT) X-Originating-IP: [69.91.158.134] In-Reply-To: References: <4C9385B0.2080909@shatow.net> <20100917161847.GA58503@icarus.home.lan> <201009221300.o8MD0Cbm030033@higson.cam.lispworks.com> Date: Wed, 22 Sep 2010 10:19:22 -0700 Message-ID: From: David Brodbeck To: freebsd-fs@freebsd.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Subject: Re: what happens to pool if ZIL dies on ZFS v14 X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 22 Sep 2010 17:19:24 -0000 On Wed, Sep 22, 2010 at 10:14 AM, David Brodbeck wrote: > On Wed, Sep 22, 2010 at 6:00 AM, Martin Simmons wr= ote: >>>>>>> On Tue, 21 Sep 2010 15:38:22 -0700, David Brodbeck said: >>> >>> If you don't have a separate log device, synchronous writes are very >>> slow with the ZIL enabled. =A0This isn't such a big deal unless you're >>> using NFS, where essentially every write is synchronous. >> >> Is that true for all versions of NFS? =A0In my experience (on 8.0-RELEAS= E), >> NFSv2 is indeed synchronous, but NFSv3 does asynchronous flushing (for a >> variety of different client OSes). > > It does allow clients to request asynchronous flushing. =A0My statement > that "essentially every write is synchronous" was a bit of an > overstatement; the problem comes when the client issues a COMMIT, > which happens frequently when doing some operations, such as > extracting tar files. =A0These are the operations that can get quite > slow when using NFS with the ZIL enabled and no separate log device. > By "quite slow," I mean several minutes to extract a tar file that > takes less than a minute with the ZIL disabled. I should add that there's a very good, if somewhat OpenSolaris-centric, explanation of the issue here: http://blogs.sun.com/roch/entry/nfs_and_zfs_a_fine The problem shows up more with ZFS because it enforces proper cache semantics, while many other filesystems do not. This isn't always a satisfactory explanation to users who expect to be able to untar files in a reasonable amount of time, however. ;)