From owner-freebsd-fs@FreeBSD.ORG Sun Oct 16 18:02:11 2011 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 AA7BB106564A for ; Sun, 16 Oct 2011 18:02:11 +0000 (UTC) (envelope-from luchesar.iliev@gmail.com) Received: from mail-ey0-f182.google.com (mail-ey0-f182.google.com [209.85.215.182]) by mx1.freebsd.org (Postfix) with ESMTP id 3463C8FC08 for ; Sun, 16 Oct 2011 18:02:10 +0000 (UTC) Received: by eyd10 with SMTP id 10so3039725eyd.13 for ; Sun, 16 Oct 2011 11:02:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=message-id:disposition-notification-to:date:from:user-agent :mime-version:to:cc:subject:references:in-reply-to :x-enigmail-version:openpgp:content-type:content-transfer-encoding; bh=QOOUgb8RcyyrpwaS1VzsZRQpmbZEqK6Tc2R46U2qG9c=; b=V4gDDt1u4QTh/5qXyxdiZ88fEYjD08zQRHuxXsa9tualP7SY4luRT6Uv9CBR7FJcHN +AiuiDWB6DLbzPxNPoZ4wItjfnVJ5o12ymyscQC6m8u0s0mj9WJb8yeiuxiPXkONIeWD aX96I5tU6PubuXBTPh7gQvi3eg4Vkfntxy5f0= Received: by 10.223.17.11 with SMTP id q11mr19125531faa.13.1318788129324; Sun, 16 Oct 2011 11:02:09 -0700 (PDT) Received: from [79.124.93.41] ([79.124.93.41]) by mx.google.com with ESMTPS id m26sm18516987fac.6.2011.10.16.11.02.07 (version=SSLv3 cipher=OTHER); Sun, 16 Oct 2011 11:02:08 -0700 (PDT) Message-ID: <4E9B1C1E.7090804@gmail.com> Date: Sun, 16 Oct 2011 21:02:06 +0300 From: "Luchesar V. ILIEV" User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:7.0.1) Gecko/20111002 Thunderbird/7.0.1 MIME-Version: 1.0 To: Daniel Kalchev , Patrick Donnelly References: <4E9AE725.4040001@gmail.com> <169E82FD-3B61-4CAB-B067-D380D69CDED5@digsys.bg> In-Reply-To: <169E82FD-3B61-4CAB-B067-D380D69CDED5@digsys.bg> X-Enigmail-Version: undefined OpenPGP: id=9A1FEEFF; url=https://cert.acad.bg/pgp-keys/ Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Cc: freebsd-fs@freebsd.org Subject: Re: [ZFS] Using SSD with partitions 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: Sun, 16 Oct 2011 18:02:11 -0000 On 16/10/2011 19:17, Daniel Kalchev wrote: > > On Oct 16, 2011, at 17:16 , Luchesar V. ILIEV wrote: > >> 6. If, OTOH, you're running a reasonably recent -STABLE (8 or 9), >> then your zpool version is likely 28 (thanks, pjd@), which means >> ZIL is not that scary, but you might still lose some data. Even an >> unexpected power failure might cause trouble, unless the SSD is >> designed to handle it gracefully (this typically involves some sort >> of capacitor). > > Just for the record: even without ZIL, you will most definitely lose > data at power outage. In most cases, this will not damage the ZFS > filesystem, but data will be lost. There is nothing that can prevent > this. > > Therefore, with ZFS v28, adding ZIL does not introduce any more risk > to your data. I might be wrong in my interpretation, but from what I remember, when the power goes down, an unprotected SSD is likely to lose _more_ data than simply its write buffers -- that's quite unlike a hard-drive. So much, in fact, that the whole ZIL might become corrupted (and that's potentially way more data than any device cache). _If_ that's true, then isn't an array of only "conventional" HDDs, where the ZIL is interleaved with the zpool itself, at least a bit safer from power failures? Again, if we are taking the cheaper SSDs into account. > One thing to have in mind is ZIL will help only under certain > workloads, sequential write is not one of these. It helps most with > database-type loads and sync writes like an NFS server that is > written heavily. Freddie have good advice on determining if it will > help. > > L2ARC on the other hand may help enormously, especially if the spool > is big. Workstation-class motherboards until recently were topped at > 8GB RAM and ZFS is happy with as much RAM as you can offer. Adding > L2ARC may provide more headroom. Benefits of course depend on the > workload. Neither L2ARC or ZIL provide magical benefits. Which is yet another reason to go for more RAM, as it tends to be quite magic-yielding. Just kidding here, but, seriously, if Patrick has room for some RAM upgrade, I think he should consider this, at least for performance (a boot and OS drive, obviously, are another matter). Cheers, Luchesar