From owner-freebsd-questions@freebsd.org Fri Aug 28 09:14:32 2015 Return-Path: Delivered-To: freebsd-questions@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 678E29C39FC for ; Fri, 28 Aug 2015 09:14:32 +0000 (UTC) (envelope-from m.seaman@infracaninophile.co.uk) Received: from smtp.infracaninophile.co.uk (smtp.infracaninophile.co.uk [IPv6:2001:8b0:151:1:3cd3:cd67:fafa:3d78]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (Client CN "smtp.infracaninophile.co.uk", Issuer "infracaninophile.co.uk" (not verified)) by mx1.freebsd.org (Postfix) with ESMTPS id 10C191C2E for ; Fri, 28 Aug 2015 09:14:31 +0000 (UTC) (envelope-from m.seaman@infracaninophile.co.uk) Received: from ox-dell39.ox.adestra.com (no-reverse-dns.metronet-uk.com [85.199.232.226] (may be forged)) (authenticated bits=0) by smtp.infracaninophile.co.uk (8.15.2/8.15.2) with ESMTPSA id t7S9EJwn009156 (version=TLSv1.2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128 verify=NO); Fri, 28 Aug 2015 10:14:20 +0100 (BST) (envelope-from m.seaman@infracaninophile.co.uk) Authentication-Results: smtp.infracaninophile.co.uk; dmarc=none header.from=infracaninophile.co.uk DKIM-Filter: OpenDKIM Filter v2.10.3 smtp.infracaninophile.co.uk t7S9EJwn009156 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=infracaninophile.co.uk; s=201001-infracaninophile; t=1440753260; bh=vxJw3ilQ+bfadX8ak0aO2O853pv5mo8NOIzedHSm0OY=; h=Subject:To:References:From:Date:In-Reply-To; z=Subject:=20Re:=20Replacing=20Drive=20with=20SSD|To:=20Matt=20Smit h=20,=20freebsd-questions@freebsd.org|References: =20=0D=0A=20<55E01D AE.1020709@infracaninophile.co.uk>=20<20150828084643.GB1274@xtaz.u k>|From:=20Matthew=20Seaman=20|Da te:=20Fri,=2028=20Aug=202015=2010:14:19=20+0100|In-Reply-To:=20<20 150828084643.GB1274@xtaz.uk>; b=Ph/WBUf/J0ws6KQcsTSDy/LtGtKAM3+YMKU4eFXvOeUJKaZWoZMY/0heLobhLh9+F nPXsS/OjHrzR+RfrDe3N7C1TBAutHK742iuPVgPaKD9PxcW3Rey5O1wmEmPvOaE6GN ts0bZQIuKkw5hOSQYmfHmgjdVUWxLo3Xk373LuOg= X-Authentication-Warning: lucid-nonsense.infracaninophile.co.uk: Host no-reverse-dns.metronet-uk.com [85.199.232.226] (may be forged) claimed to be ox-dell39.ox.adestra.com Subject: Re: Replacing Drive with SSD To: Matt Smith , freebsd-questions@freebsd.org References: <55E01DAE.1020709@infracaninophile.co.uk> <20150828084643.GB1274@xtaz.uk> From: Matthew Seaman X-Enigmail-Draft-Status: N1110 Message-ID: <55E0266B.10005@infracaninophile.co.uk> Date: Fri, 28 Aug 2015 10:14:19 +0100 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:38.0) Gecko/20100101 Thunderbird/38.2.0 MIME-Version: 1.0 In-Reply-To: <20150828084643.GB1274@xtaz.uk> Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="srx7SIHoEg7JF4uHnvIaPMEwicsa3k0Ta" X-Virus-Scanned: clamav-milter 0.98.7 at lucid-nonsense.infracaninophile.co.uk X-Virus-Status: Clean X-Spam-Status: No, score=-1.5 required=5.0 tests=ALL_TRUSTED,AWL,BAYES_00, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU autolearn=ham autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on lucid-nonsense.infracaninophile.co.uk X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.20 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 28 Aug 2015 09:14:32 -0000 This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --srx7SIHoEg7JF4uHnvIaPMEwicsa3k0Ta Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 08/28/15 09:46, Matt Smith wrote: > I've heard a rumour that you should never use dd with SSD drives becaus= e > of the wear levelling stuff. Apparently SSDs automatically make sure > that data is sent to unused flash cells so that all the cells wear > evenly, but if you use dd on them it makes them think that every single= > cell is in use which screws this up? Hmmm.... Yes, dd will copy all of the source disk including disk blocks that are unused, empty space. Overwriting a cell that is already zeroes with yet more zeroes is a waste of time, but I don't know if that would actually use up some of the life of that cell. It shouldn't confuse the wear-levelling code on the drive particularly -- it might take a little while to sort itself out after the fact, but it's no worse conceptually than filling the drive up with a big file and then deleting that file. So, avoid using dd if you can, but it's probably not a disaster if you can't avoid it. Cheers, Matthew --srx7SIHoEg7JF4uHnvIaPMEwicsa3k0Ta Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIcBAEBCgAGBQJV4CZrAAoJEABRPxDgqeTnKowP/Rdx+1OxnUqu7s+p7nfdYlMy h7iirdhGsCZQW8ht3fPoRmslORPwcVR4jpIz6neFaYYJKi/DPUmUX7ru3vBfjoKc DCGB61UqKPcX4ld+uyjipRGh6QR4uZXb2kzPU2m4LuSxk/zgjmyBNzxYn5cYLPP2 w8kUSBOooOXJns+iAlvnzAvGscwKdevtP56116cHab/LH5mF+7OpvK7K/b4YboLO ++lZ3pY8URdp0a+e0hEgrGWLnttfVWvFLsSm0qGbP4TWUqxqSZeyCqT/MxJiScPh fZhvxTUbwm6PQGDKVEqjdN3GlDVmecxxRTmN3EDqgWDdb7HAmvDeXIQV0x0foEC5 /BBQ7T21bgxV3PAnZiRY+uLp9SN+xSWTe89T0Etg3QV7YavGi1Sr7yFQnopxriiw k5ohAR6brnt8/24snC8V8bIj98Bl0sEhO8AI43+ZjXOgear7LXzFZ7vaE7zMi2k1 K+stWm7Yq4dl1mVrsAb/l9xLd3+rQdYQSN3W3zuj16ox5DmFxCjZB1ik2KioFk3f trQDCEQEBVJ2RGVDJprhFnbdTT9+VO8Sa0OmzAHC7nT0/KWmiUb9XfgWJ0ozWfhn F/qdkS57yTsPTC/bSSivxG87nZl2e6acXslhQpL/0t53yaNSDPo6EP1vUichFC6a 2z+2ZtnG8bNUrISMghIW =sIaV -----END PGP SIGNATURE----- --srx7SIHoEg7JF4uHnvIaPMEwicsa3k0Ta--