From owner-freebsd-stable@FreeBSD.ORG Sat Nov 3 23:16:03 2012 Return-Path: Delivered-To: stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id BCDCC7B0 for ; Sat, 3 Nov 2012 23:16:03 +0000 (UTC) (envelope-from jroberson@jroberson.net) Received: from mail-pa0-f54.google.com (mail-pa0-f54.google.com [209.85.220.54]) by mx1.freebsd.org (Postfix) with ESMTP id 835158FC0A for ; Sat, 3 Nov 2012 23:16:03 +0000 (UTC) Received: by mail-pa0-f54.google.com with SMTP id bi1so3349845pad.13 for ; Sat, 03 Nov 2012 16:16:03 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20120113; h=date:from:x-x-sender:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version:content-type:x-gm-message-state; bh=84euiro70ju3Z6WtfDCQOWgK2nyyflkeDZ06pg+DuXc=; b=koLUJKxdhKtpvvHIwR/TE8CI5heq7FjmD3S1lZgoDXgglawaWpttvslRrFU49gIjiv RZzOtnN+WklvsyLPa8AWQyjEVhIZV5NNS8mKhejbveUudYjGXiEvqDOSVbhHdmIucM9/ Qqp3Wt6owV6aAhUBvQtEFEZzOLFbebat5hXq+/h1ft4j2HNMM1kxTWcenXGh5y3aYJbl Pq+lGv1GhPW2sCOeDmbZjvYiT0o8KAQEYkpSMYHRzhiMlOST/RgoZw/t9t84S9Xl2pvu eDOzL2jdxZyHYsMueZNwnB20848/v+xgp7R3N91+aHWgsUVDqLO0QU7rF5jd++Cpy2Q8 C74A== Received: by 10.68.248.33 with SMTP id yj1mr18502733pbc.141.1351984562927; Sat, 03 Nov 2012 16:16:02 -0700 (PDT) Received: from rrcs-66-91-135-210.west.biz.rr.com (rrcs-66-91-135-210.west.biz.rr.com. [66.91.135.210]) by mx.google.com with ESMTPS id n11sm7990699pby.67.2012.11.03.16.16.01 (version=SSLv3 cipher=OTHER); Sat, 03 Nov 2012 16:16:02 -0700 (PDT) Date: Sat, 3 Nov 2012 13:14:38 -1000 (HST) From: Jeff Roberson X-X-Sender: jroberson@desktop To: Ian Lepore Subject: Re: Why is SU+J undesirable on SSDs? In-Reply-To: <1351983269.1120.137.camel@revolution.hippie.lan> Message-ID: References: <201211032130.PAA04484@lariat.net> <1351983269.1120.137.camel@revolution.hippie.lan> User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Gm-Message-State: ALoCoQlSPGoz6qhflhEOqzBoWMykmM49/6y1C5heXAjtIlqSz6uyx9Kv0N39CmJVek1Q+gbQbqVs Cc: Adam Vande More , stable@freebsd.org, Brett Glass X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 03 Nov 2012 23:16:04 -0000 On Sat, 3 Nov 2012, Ian Lepore wrote: > On Sat, 2012-11-03 at 17:06 -0500, Adam Vande More wrote: >> On Sat, Nov 3, 2012 at 4:30 PM, Brett Glass wrote: >> >>> Have been following the thread related to SU+J, and am wondering: why is it >>> considered to be undesirable on SSDs (assuming that they have good wear >>> leveling)? >> >> >> Superstition >> >> > > Yeah, that's what it must be. Or... it could be well-informed choice. > > Journaling increases the number of writes. That puts wear on any disk, > mechanical or SSD, and it takes time. What it buys you is better > performance if you get into a crash recovery situation. It's perfectly > reasonable for someone to make the decision that their SSD can finish an > fsck so fast that there's no point in paying any penalty for the extra > writes for journaling. The journal entries are 32 bytes per in SUJ. So the number of extra writes is down in the noise. The journaling also gets you asynchronous partial truncation and a few other asynchronous operations that are sync in SU. It does cost slightly more cpu time and more memory. I'm not saying you're making the wrong choice. I'm just saying that it's not clear that you should or should not use it with SSDs. > > I have a 256G SSD here with about 200G of data on it, and fsck without > journaling takes about 3 minutes. I can live with that. With more data > or a slower drive I might make a different choice. If you are happy with 3 minutes this is very reasonable and I assume you turn off bg fsck. Jeff > > -- Ian > > > _______________________________________________ > freebsd-stable@freebsd.org mailing list > http://lists.freebsd.org/mailman/listinfo/freebsd-stable > To unsubscribe, send any mail to "freebsd-stable-unsubscribe@freebsd.org" >