Received: from malur.postgresql.org ([217.196.149.56]) by arkaria.postgresql.org with esmtp (Exim 4.72) (envelope-from ) id 1TibpC-0006SC-FV for pgsql-performance@arkaria.postgresql.org; Wed, 12 Dec 2012 02:13:30 +0000 Received: from localhost ([127.0.0.1] helo=postgresql.org) by malur.postgresql.org with smtp (Exim 4.72) (envelope-from ) id 1TibpB-0007LC-Ae for pgsql-performance@arkaria.postgresql.org; Wed, 12 Dec 2012 02:13:29 +0000 Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29]) by malur.postgresql.org with esmtp (Exim 4.72) (envelope-from ) id 1TibpA-0007Kf-5x for pgsql-performance@postgresql.org; Wed, 12 Dec 2012 02:13:28 +0000 Received: from mail-la0-f51.google.com ([209.85.215.51]) by magus.postgresql.org with esmtp (Exim 4.72) (envelope-from ) id 1Tibp7-00047I-L7 for pgsql-performance@postgresql.org; Wed, 12 Dec 2012 02:13:27 +0000 Received: by mail-la0-f51.google.com with SMTP id e4so109438lag.24 for ; Tue, 11 Dec 2012 18:13:25 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=content-type:mime-version:subject:from:in-reply-to:date:cc :message-id:references:to:x-mailer; bh=B2t9hJnvBTg3FevmtMigB07s2xP/6x+PVqjUqLHUJSM=; b=m6ZzCIfd7fn/Sl153RR/urXWmS5I52/Z0LdI/nemWDcN7w/tCj1wjVW9G3GFUavEq7 YRLdXMdww0vQZYQhEPLV0ck+DlvxDv5zuz2Em2fcH3yLqQHH+FMCB/4g/viM+7/7y+HC Ks3nMn5/yh4VZneTE1sh06EFewvIrE8bbCTL1ZgyqPEeuej3eEeA0/tNKBo4pvT7QWKl 9rq4NelKbWFxQxNXlrjYDwyDT+0rcxOgGSSR2FecuxNsB03kPPOLiVBLq2fFkGbwqH4y ueejImUSmwvv/Tsr0r6NrP3Ua53Le59s+ZmTqEW38PxbXPnYnJpb9FJfj2BTgd85ikOq Tjhg== Received: by 10.152.106.171 with SMTP id gv11mr139299lab.26.1355278404859; Tue, 11 Dec 2012 18:13:24 -0800 (PST) Received: from [192.168.20.5] ([176.195.39.85]) by mx.google.com with ESMTPS id fb1sm10001893lbb.15.2012.12.11.18.13.23 (version=TLSv1/SSLv3 cipher=OTHER); Tue, 11 Dec 2012 18:13:24 -0800 (PST) Content-Type: multipart/alternative; boundary="Apple-Mail=_24AC0594-2DA6-4BD0-B2DA-AC02E661166C" Mime-Version: 1.0 (Mac OS X Mail 6.2 \(1499\)) Subject: Re: Do I have a hardware or a software problem? From: Evgeny Shishkin In-Reply-To: <50C7E598.2070902@2ndQuadrant.com> Date: Wed, 12 Dec 2012 06:13:22 +0400 Cc: =?iso-8859-1?Q?Niels_Kristian_Schj=F8dt?= , Jeff Janes , "pgsql-performance@postgresql.org" Message-Id: <8A08ED7E-CF78-4F40-ACF1-1C87CEBBD00A@gmail.com> 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> <50C7DDDE.1000000@2ndQuadrant.com> <3ADBD9A3-966F-40E8-AF78-0F2093D79BEE@gmail.com> <50C7E598.2070902@2ndQuadrant.com> To: Craig Ringer X-Mailer: Apple Mail (2.1499) X-Pg-Spam-Score: -2.7 (--) 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 --Apple-Mail=_24AC0594-2DA6-4BD0-B2DA-AC02E661166C Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 On Dec 12, 2012, at 6:02 AM, Craig Ringer wrote: > On 12/12/2012 09:44 AM, Evgeny Shishkin wrote: >> So far, more than a year already, i bought consumer ssds with = 300-400$ hw raid. Cost effective and fast, may be not very safe, but so = far so good. All data protection measures from postgresql are on, of = course. >=20 > You're aware that many low end SSDs lie to the RAID controller about = having written data, right? Even if the RAID controller sends a flush = command, the SSD might cache the write in non-durable cache. If you're = using such SSDs and you lose power, data corruption is extremely likely, = because your SSDs are essentially ignoring fsync. >=20 > Your RAID controller's BBU won't save you, because once the disks tell = the RAID controller the data has hit durable storage, the RAID = controller feels free to flush it from its battery backed cache. If the = disks are lying... >=20 > The only solid way to find out if this is an issue with your SSDs is = to do plug-pull testing and find out. >=20 Yes, i am aware of this issue. Never experienced this neither on intel = 520, no ocz vertex 3. Have you heard of them on this list? > --=20 > Craig Ringer http://www.2ndQuadrant.com/ > PostgreSQL Development, 24x7 Support, Training & Services --Apple-Mail=_24AC0594-2DA6-4BD0-B2DA-AC02E661166C Content-Transfer-Encoding: 7bit Content-Type: text/html; charset=windows-1252
On Dec 12, 2012, at 6:02 AM, Craig Ringer <craig@2ndQuadrant.com> wrote:

On 12/12/2012 09:44 AM, Evgeny Shishkin wrote:
So far, more than a year already, i bought consumer ssds with 300-400$ hw raid. Cost effective and fast, may be not very safe, but so far so good. All data protection measures from postgresql are on, of course.

You're aware that many low end SSDs lie to the RAID controller about having written data, right? Even if the RAID controller sends a flush command, the SSD might cache the write in non-durable cache. If you're using such SSDs and you lose power, data corruption is extremely likely, because your SSDs are essentially ignoring fsync.

Your RAID controller's BBU won't save you, because once the disks tell the RAID controller the data has hit durable storage, the RAID controller feels free to flush it from its battery backed cache. If the disks are lying...

The only solid way to find out if this is an issue with your SSDs is to do plug-pull testing and find out.


Yes, i am aware of this issue. Never experienced this neither on intel 520, no ocz vertex 3.
Have you heard of them on this list?
-- 
 Craig Ringer                   http://www.2ndQuadrant.com/
 PostgreSQL Development, 24x7 Support, Training & Services

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