Date: Fri, 28 Aug 2015 10:14:19 +0100 From: Matthew Seaman <m.seaman@infracaninophile.co.uk> To: Matt Smith <fbsd@xtaz.co.uk>, freebsd-questions@freebsd.org Subject: Re: Replacing Drive with SSD Message-ID: <55E0266B.10005@infracaninophile.co.uk> In-Reply-To: <20150828084643.GB1274@xtaz.uk> References: <CEAD84AD-341A-4FB9-A3A1-D0D5A550AFFD@lafn.org> <55E01DAE.1020709@infracaninophile.co.uk> <20150828084643.GB1274@xtaz.uk>
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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--
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