Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtp (Exim 4.72) (envelope-from ) id 1Tib8N-0005n1-V5 for pgsql-performance@arkaria.postgresql.org; Wed, 12 Dec 2012 01:29:16 +0000 Received: from localhost ([127.0.0.1] helo=postgresql.org) by malur.postgresql.org with smtp (Exim 4.72) (envelope-from ) id 1Tib8M-0004pL-Fk for pgsql-performance@arkaria.postgresql.org; Wed, 12 Dec 2012 01:29:14 +0000 Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29]) by malur.postgresql.org with esmtp (Exim 4.72) (envelope-from ) id 1Tib8L-0004pF-Cv for pgsql-performance@postgresql.org; Wed, 12 Dec 2012 01:29:13 +0000 Received: from outmail148113.authsmtp.com ([62.13.148.113]) by magus.postgresql.org with esmtp (Exim 4.72) (envelope-from ) id 1Tib8J-0003RV-BY for pgsql-performance@postgresql.org; Wed, 12 Dec 2012 01:29:12 +0000 Received: from mail-c232.authsmtp.com (mail-c232.authsmtp.com [62.13.128.232]) by punt10.authsmtp.com (8.14.2/8.14.2/Kp) with ESMTP id qBC1T9KL077241; Wed, 12 Dec 2012 01:29:09 GMT Received: from ayaki.localdomain (58-7-194-83.dyn.iinet.net.au [58.7.194.83]) (authenticated bits=0) by mail.authsmtp.com (8.14.2/8.14.2/) with ESMTP id qBC1T3D2064034 (version=TLSv1/SSLv3 cipher=DHE-RSA-CAMELLIA256-SHA bits=256 verify=NO); Wed, 12 Dec 2012 01:29:06 GMT Message-ID: <50C7DDDE.1000000@2ndQuadrant.com> Date: Wed, 12 Dec 2012 09:29:02 +0800 From: Craig Ringer Organization: 2nd Quadrant User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/17.0 Thunderbird/17.0 MIME-Version: 1.0 To: Evgeny Shishkin CC: =?windows-1252?Q?Niels_Kristian_Schj=F8dt?= , Jeff Janes , "pgsql-performance@postgresql.org" Subject: Re: Do I have a hardware or a software problem? References: <8F7661E7-D6D4-4334-8C6A-A8B6C56A2C3F@autouncle.com> <50C7351C.30407@2ndQuadrant.com> <4507A68A-3CD5-4283-AFA5-1C0593427E14@autouncle.com> <67FBF3AF-5C6A-45D4-9206-7257C8C01C5E@gmail.com> <50C7D7D2.4070605@2ndQuadrant.com> <2BCB6843-1396-42C9-A5BF-21C7C978FF4B@gmail.com> In-Reply-To: <2BCB6843-1396-42C9-A5BF-21C7C978FF4B@gmail.com> X-Enigmail-Version: 1.4.6 Content-Type: multipart/alternative; boundary="------------060609070301040803050804" X-Server-Quench: 52ab84be-43fb-11e2-b10b-0025903375e2 X-AuthReport-Spam: If SPAM / abuse - report it at: http://www.authsmtp.com/abuse X-AuthRoute: OCdxZQATClZeVg0b BQteCiN5VAwpPBRK HVkIKg5MJUcNSQVJ NksachtFaQdbaVxS HGQLWlZEUFx7W2p/ aw0faA1DZVRPVgF0 WEtWQFdQERppT11z dR96UW1wdwNCeH10 K0RiWnNbEkF4JBR1 RhwBCGkFMzV9aWFK Ul0KdgMGbQNKfBpM alN8U3ZYYytlM3Bw LDceBR4WBxBqYAhS CiBFLVsMTA4CVj41 XRwdFC8iVUofDyx7 NBsoNkEVBktZKl81 O18sXAVw X-Authentic-SMTP: 61633235383639.1019:706 X-AuthFastPath: 0 (Was 255) X-AuthSMTP-Origin: 58.7.194.83/2525 X-AuthVirus-Status: No virus detected - but ensure you scan with your own anti-virus system. X-Pg-Spam-Score: -2.6 (--) List-Archive: List-Help: List-ID: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: X-Mailing-List: pgsql-performance Precedence: bulk Sender: pgsql-performance-owner@postgresql.org This is a multi-part message in MIME format. --------------060609070301040803050804 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit On 12/12/2012 09:17 AM, Evgeny Shishkin wrote: > > Actually most of low-end SSDs don't do write caching, they do not have > enough ram for that. Sandforce for example. > Or, worse, some of them do limited write caching but don't protect their write cache from power loss. Instant data corruption! I would be extremely reluctant to use low-end SSDs for a database server. > If we are talking about dedicated machine for database with ssd > drives, why would anybody don't by hardware raid for about 500-700$? I'd want to consider whether the same money is better spent on faster, higher quality SSDs with their own fast write caches. -- Craig Ringer http://www.2ndQuadrant.com/ PostgreSQL Development, 24x7 Support, Training & Services --------------060609070301040803050804 Content-Type: text/html; charset=windows-1252 Content-Transfer-Encoding: 7bit
On 12/12/2012 09:17 AM, Evgeny Shishkin wrote:

Actually most of low-end SSDs don't do write caching, they do not have enough ram for that. Sandforce for example.

Or, worse, some of them do limited write caching but don't protect their write cache from power loss. Instant data corruption!

I would be extremely reluctant to use low-end SSDs for a database server.

If we are talking about dedicated machine for database with ssd drives, why would anybody don't by hardware raid for about 500-700$?
I'd want to consider whether the same money is better spent on faster, higher quality SSDs with their own fast write caches.

-- 
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services
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