From owner-freebsd-questions@FreeBSD.ORG Sun Jul 29 00:14:32 2012 Return-Path: Delivered-To: freebsd-questions@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [69.147.83.52]) by hub.freebsd.org (Postfix) with ESMTP id E3274106564A for ; Sun, 29 Jul 2012 00:14:32 +0000 (UTC) (envelope-from rwmaillists@googlemail.com) Received: from mail-we0-f182.google.com (mail-we0-f182.google.com [74.125.82.182]) by mx1.freebsd.org (Postfix) with ESMTP id 65B728FC08 for ; Sun, 29 Jul 2012 00:14:32 +0000 (UTC) Received: by weyx56 with SMTP id x56so3399935wey.13 for ; Sat, 28 Jul 2012 17:14:31 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=googlemail.com; s=20120113; h=date:from:to:subject:message-id:in-reply-to:references:x-mailer :mime-version:content-type:content-transfer-encoding; bh=xbkw6V37WRQ298MJHsdKAhJhz3bv1Zwm4IGFl0Z27HY=; b=NyiQB2X32zwsl9bcisZ0Wf8vSzWwoDzTnjy8bEqicciMEScD4AMnSJaLrSB2DE55I3 pE6XEF2JTOlZ/TARCGqZVMMk8UCo2300rm0owkE/Ran8YrPBdnzUpajXXUGkULgeyERd ZVusL7Z+2rWjJjxaneZMnv+sMZvcm0izvJaNAJl5v93MCzEgCzAduIKaBHOXNm+DNOAB 7nWEkHhhe9U82apyKJmAz9R2QzDxpJH5fq/0QwDyNk+DBQISH0nDBnTix+QhPEajaa2k dD1VwdgYlFbTRJHLG4evUmiRl+mYRHVG0+NZGtGy9piB/3nYPPOEQLiqrxbgCRlhAgqh yZpQ== Received: by 10.216.116.70 with SMTP id f48mr3353163weh.162.1343520871357; Sat, 28 Jul 2012 17:14:31 -0700 (PDT) Received: from gumby.homeunix.com (87-194-105-247.bethere.co.uk. [87.194.105.247]) by mx.google.com with ESMTPS id w7sm7399899wiz.0.2012.07.28.17.14.29 (version=SSLv3 cipher=OTHER); Sat, 28 Jul 2012 17:14:30 -0700 (PDT) Date: Sun, 29 Jul 2012 01:14:26 +0100 From: RW To: freebsd-questions@freebsd.org Message-ID: <20120729011426.0d31fe19@gumby.homeunix.com> In-Reply-To: References: X-Mailer: Claws Mail 3.8.1 (GTK+ 2.24.6; amd64-portbld-freebsd8.3) Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Subject: Re: FreeBSD on SSD X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 29 Jul 2012 00:14:33 -0000 On Sat, 28 Jul 2012 20:22:11 +0200 (CEST) Wojciech Puchar wrote: > > The read-cache idea is very sound, mainly because by using it this > > way Seagate would not have to create a special set of instructions > > for installing and using the HDD. >=20 > I don't think that this drive cache is smart enough to really cache > needed things and not flush that cache with useless data too often. >=20 =46rom what I've read the cache is divided into two part. One part holds blocks that are consistently read during boot-ups. The other part holds short runs of data that have been read off the disk with long access times. There's an oldish FAQ here:=20 http://forums.seagate.com/t5/Momentus-XT-Momentus-Momentus/Momentus-XT-Freq= uently-Asked-Questions/m-p/52701 Note question 6 "Internal tests were conducted using a script that mimics 250GB of data written to the drive every day for 5 years, and the Flash in Seagate=E2=80=99s unique solution showed no signs of degredation. If the Flash ever fails, the data is never lost because it is mirrored to the disk and the drive would continue to operate as a traditional 7200RPM drive with 32MB of DRAM cache." >=20 > > My final question would be : > >=20 > > Seeing as the HDD only has a SATA connector, this would mean that > > the SSD part already has a memory control device that regulates > > access to that sector, whether it is a plain read-cache or not. > > This would imply that FreeBSD could communicate with the HDD > > normally, through the SATA connector, just like any regular HDD. >=20 > indeed. >=20 > Such a drive is a good idea, but complete lack of documentation (how > it operate) is not. >=20 > You have to guess how this SSD-cache works because it is not > documented. Well, it is intended to be completely transparent. >=20 > the other thing is erasing data. You want to sell that drive and > clear your data by >=20 > dd if=3D/dev/zero of=3D/dev/disk bs=3D1m >=20 > but does it clear SSD cache? That isn't guaranteed to clear any modern disk since they started using spare sectors > i don't think so. Someone sophisticated=20 > enough would perform raw read of cache chips and get cached data, > which can actually be the most important part=20 If you're that paranoid use geli, or don't sell.=20