From owner-freebsd-fs@FreeBSD.ORG Wed Jun 22 11:42:28 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 F39B4106566B for ; Wed, 22 Jun 2011 11:42:27 +0000 (UTC) (envelope-from frimik@gmail.com) Received: from mail-vx0-f182.google.com (mail-vx0-f182.google.com [209.85.220.182]) by mx1.freebsd.org (Postfix) with ESMTP id AD6938FC1A for ; Wed, 22 Jun 2011 11:42:27 +0000 (UTC) Received: by vxg33 with SMTP id 33so721047vxg.13 for ; Wed, 22 Jun 2011 04:42:27 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:mime-version:in-reply-to:references:date :message-id:subject:from:to:cc:content-type; bh=dp+0NpaiQzACfmOz1W8ZUMZmoKnJaLtd351LPf+xnlg=; b=pPX7gQ9Jy418EmYy5WbIuNpy/nAe08gh/I+KOvRW2xs6b369JVg2IzPE75r5eZNlfr Zcj8VfazPh7BtMNEjV3+dPt8m+CDPxNoQFU5InV23OQarCNgbx/GvaPQhD+/tE/g5oXg dv1xF6m4k6h7mxlaPpv66UZO2xrRLv295w7F8= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type; b=RkEzV6aRmmu5JVdxcYqw9zNnOV4fIVgG/RSH04pA+J5wy/VVn6n00PjgLkT1TZcW+B 4D+AABIm1ZV2REINjqg7gGnmMIvsuvTTeFpETg4mZ8jPJyJAO0eRJylTfyQEMhnA+bFJ KM/YzEsOlg7515I6bWL98xTO5vl5s0Wy561xA= MIME-Version: 1.0 Received: by 10.220.147.201 with SMTP id m9mr183723vcv.264.1308741505209; Wed, 22 Jun 2011 04:18:25 -0700 (PDT) Received: by 10.220.100.138 with HTTP; Wed, 22 Jun 2011 04:18:25 -0700 (PDT) In-Reply-To: References: Date: Wed, 22 Jun 2011 13:18:25 +0200 Message-ID: From: Mikael Fridh To: Wiktor Niesiobedzki Content-Type: text/plain; charset=ISO-8859-1 Cc: freebsd-fs@freebsd.org Subject: Re: ZFS L2ARC hit ratio 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 Jun 2011 11:42:28 -0000 On Wed, Jun 22, 2011 at 6:51 AM, Wiktor Niesiobedzki wrote: > 2011/6/22 Artem Belevich : >> >> L2ARC is filled with items evicted from ARC. The catch is that L2ARC >> writes are intentionally throttled. When L2ARC is empty writes happen >> at a higher rate, but it's still intentionally low so that >> read-optimized cache device does not wear out too soon. The bottom >> line is that not all the data spilled out of ARC ends up in L2ARC on >> the first try. Re-run your experiment again and you would probably see >> some improvement in L2ARC hit rates. > > I've run the experiment 3 times with no extent. Funny thing is: > - in first run, I see a lot of write activity against cache device > - in second run, I see no write activity against cache device, nor read activity What about read activity from vdevs? > So my guess is, that anyhow, ZFS cache layer knows, that this file is > *there*, though it decides not to serve it from L2ARC... Have you considered, that it is mostly served from ARC? Or even from the underlying vdevs? How much RAM have you got? And thus; How big is your ARC :) -- Mikael