Received: from maia.hub.org (maia-3.hub.org [200.46.204.243]) by mail.postgresql.org (Postfix) with ESMTP id AA3E9B5DBCA for ; Sun, 17 Jul 2011 23:30:51 -0300 (ADT) Received: from mail.postgresql.org ([200.46.204.86]) by maia.hub.org (mx1.hub.org [200.46.204.243]) (amavisd-maia, port 10024) with ESMTP id 86577-03 for ; Mon, 18 Jul 2011 02:30:45 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from www.postnewspapers.com.au (www.postnewspapers.com.au [173.230.139.50]) by mail.postgresql.org (Postfix) with ESMTP id 7AAD6B5DBD1 for ; Sun, 17 Jul 2011 23:30:45 -0300 (ADT) Received: from localhost (localhost [127.0.0.1]) by www.postnewspapers.com.au (Postfix) with ESMTP id 0F11010D; Sun, 17 Jul 2011 22:30:46 -0400 (EDT) X-Virus-Scanned: amavisd-new at postnewspapers.com.au.com Received: from www.postnewspapers.com.au ([127.0.0.1]) by localhost (www.postnewspapers.com.au [127.0.0.1]) (amavisd-new, port 10024) with LMTP id M0A9TZGAX90F; Sun, 17 Jul 2011 22:30:45 -0400 (EDT) Received: from mail.postnewspapers.com.au (ppp171-128.static.internode.on.net [150.101.171.128]) by www.postnewspapers.com.au (Postfix) with ESMTP id 2796327; Sun, 17 Jul 2011 22:30:45 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mail.postnewspapers.com.au (Postfix) with ESMTP id 1AA0EAE3F9; Mon, 18 Jul 2011 10:30:44 +0800 (WST) X-Amavis-Modified: Mail body modified (using disclaimer) - mail.postnewspapers.com.au X-Virus-Scanned: Debian amavisd-new at postnewspapers.com.au Received: from mail.postnewspapers.com.au ([127.0.0.1]) by localhost (mail.postnewspapers.com.au [127.0.0.1]) (amavisd-new, port 10024) with LMTP id 3vOPjIDF+jIy; Mon, 18 Jul 2011 10:30:39 +0800 (WST) Received: from [192.168.1.24] (unknown [202.81.69.134]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "Craig Ringer", Issuer "POST Certificate Authority" (verified OK)) by mail.postnewspapers.com.au (Postfix) with ESMTPSA id B515FAE3CE; Mon, 18 Jul 2011 10:30:38 +0800 (WST) Message-ID: <4E239ABC.4020204@postnewspapers.com.au> Date: Mon, 18 Jul 2011 10:30:20 +0800 From: Craig Ringer User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:5.0) Gecko/20110624 Thunderbird/5.0 MIME-Version: 1.0 To: Andy CC: pgsql-performance@postgresql.org Subject: Re: BBU still needed with SSD? References: <1310953399.25726.YahooMailClassic@web111304.mail.gq1.yahoo.com> In-Reply-To: <1310953399.25726.YahooMailClassic@web111304.mail.gq1.yahoo.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Virus-Scanned: Maia Mailguard 1.0.1 X-Spam-Status: No, hits=-3.013 tagged_above=-10 required=5 tests=BAYES_00=-1.9, RP_MATCHES_RCVD=-1.113 X-Spam-Level: X-Archive-Number: 201107/172 X-Sequence-Number: 44384 On 18/07/2011 9:43 AM, Andy wrote: > Hi, > > Is BBU still needed with SSD? You *need* an SSD with a supercapacitor or on-board battery backup for its cache. Otherwise you *will* lose data. Consumer SSDs are like a hard disk attached to a RAID controller with write-back caching enabled and no BBU. In other words: designed to eat your data. > In this case is BBU still needed? If I put 2 SSD in software RAID 1, would that be any slower than 2 SSD in HW RAID 1 with BBU? What are the pros and cons? > You don't need write-back caching for fsync() performance if your SSDs have big enough caches. I don't know enough to say whether there are other benefits to having them on a BBU HW raid controller or whether SW RAID is fine. POST Newspapers 276 Onslow Rd, Shenton Park Ph: 08 9381 3088 Fax: 08 9388 2258 ABN: 50 008 917 717 http://www.postnewspapers.com.au/