Received: from localhost (unknown [200.46.204.183]) by postgresql.org (Postfix) with ESMTP id DF922650EBA for ; Fri, 27 Jun 2008 10:16:20 -0300 (ADT) Received: from postgresql.org ([200.46.204.86]) by localhost (mx1.hub.org [200.46.204.183]) (amavisd-maia, port 10024) with ESMTP id 78778-02 for ; Fri, 27 Jun 2008 10:16:11 -0300 (ADT) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from fk-out-0910.google.com (fk-out-0910.google.com [209.85.128.186]) by postgresql.org (Postfix) with ESMTP id 46906650E2E for ; Fri, 27 Jun 2008 10:16:15 -0300 (ADT) Received: by fk-out-0910.google.com with SMTP id e30so532249fke.3 for ; Fri, 27 Jun 2008 06:16:13 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:message-id:date:from:to :subject:cc:in-reply-to:mime-version:content-type :content-transfer-encoding:content-disposition:references; bh=Y9vxA+fE+YTRhWxoDLiMRXZs8sK3UxQ9uciXC1uOHI4=; b=xBPmJ3TRx/oCIEegXSBt8tOgDMBXbuuHN7QXSBuV97RWA02877VvnxofHwYuBw1Hn8 QlaKYHLZkFj8MIPNw7OWeAHfl6OTng3jQSRnxbLj2IYQ84xul/j1e+0KhGfb5By/sxQp KfpYUG05inEgtIODxqSNTDS2Bm2LKj3GHVEYM= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=message-id:date:from:to:subject:cc:in-reply-to:mime-version :content-type:content-transfer-encoding:content-disposition :references; b=CT/zmSrYMPCNFI7+3E/D1KrG1ylSWYSjXBWuCYWRrFKlEywi5pf4mUhloZSFIfEKxN yLaH9Mn6XeGbPrVI700kgtUPiJgrLFMeP9sgEXQWRvAW/FnUO8zElUBzY7u4HNLGCQB9 Ok3c1dA6LjqiSysguiKYNDdlcewzZ40C+l+Fo= Received: by 10.82.135.7 with SMTP id i7mr56431bud.42.1214572573458; Fri, 27 Jun 2008 06:16:13 -0700 (PDT) Received: by 10.82.147.4 with HTTP; Fri, 27 Jun 2008 06:16:13 -0700 (PDT) Message-ID: Date: Fri, 27 Jun 2008 09:16:13 -0400 From: "Merlin Moncure" To: "Matthew Wakeling" Subject: Re: Hardware vs Software RAID Cc: "Pgsql performance" In-Reply-To: MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Content-Disposition: inline References: <200806251311.m5PDBNv23559@inv.it.uc3m.es> <97454AF8-315A-4B3D-8F95-D96B190C6909@khera.org> X-Virus-Scanned: Maia Mailguard 1.0.1 X-Archive-Number: 200806/197 X-Sequence-Number: 30547 On Fri, Jun 27, 2008 at 7:00 AM, Matthew Wakeling wrote: > On Thu, 26 Jun 2008, Merlin Moncure wrote: >> >> In addition there are many different types of flash (MLC/SLC) and the >> flash cells themselves can be organized in particular ways involving various >> trade-offs. > > Yeah, I wouldn't go for MLC, given it has a tenth the lifespan of SLC. > >> The main issue is lousy random write performance that basically makes them >> useless for any kind of OLTP operation. > > For the mentioned device, they claim a sequential read speed of 100MB/s, > sequential write speed of 80MB/s, random read speed of 80MB/s and random > write speed of 30MB/s. This is *much* better than figures quoted for many > other devices, but of course unless they publish the block size they used > for the random speed tests, the figures are completely useless. right. not likely completely truthful. here's why: A 15k drive can deliver around 200 seeks/sec (under worst case conditions translating to 1-2mb/sec with 8k block size). 30mb/sec random performance would then be rough equivalent to around 40 15k drives configured in a raid 10. Of course, I'm assuming the block size :-). Unless there were some other mitigating factors (lifetime, etc), this would demonstrate that flash ssd would crush disks in any reasonable cost/performance metric. It's probably not so cut and dry, otherwise we'd be hearing more about them (pure speculation on my part). merlin