Date: Mon, 21 Mar 2016 21:47:39 -0600 From: Warner Losh <imp@bsdimp.com> To: bob prohaska <fbsd@www.zefox.net> Cc: Ian Lepore <ian@freebsd.org>, freebsd-arm@freebsd.org Subject: Re: Effect of partitioning on wear-leveling Message-ID: <E985EBE6-E062-4C5E-8F85-ECB7BDE98DE8@bsdimp.com> In-Reply-To: <20160322032832.GC83908@www.zefox.net> References: <20160321175952.GA83908@www.zefox.net> <1458586884.68920.96.camel@freebsd.org> <20160321221153.GB83908@www.zefox.net> <1458600070.68920.107.camel@freebsd.org> <20160322032832.GC83908@www.zefox.net>
next in thread | previous in thread | raw e-mail | index | archive | help
--Apple-Mail=_8C9DC301-4A05-4F2E-A703-6D525CB13CFC Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=utf-8 > On Mar 21, 2016, at 9:28 PM, bob prohaska <fbsd@www.zefox.net> wrote: >=20 > On Mon, Mar 21, 2016 at 04:41:10PM -0600, Ian Lepore wrote: >>=20 >> Also, it's been my experience that it's impossible to "wear out" an >> sdcard. I once ran a program that just wrote random data = continuously >> at full speed to a 512MB card for several months nonstop. No = noticible >> effect on the card. I actually still use that card today (in one of >> our older products whose filesystem image only needs about 40MB). >>=20 >>=20 > Have you ever checked to see how much of the 512 MB capacity remains? > Seems that quite a lot of decay wouldn't show up if you're using less > than 10% of the device's capacity. If you are writing to only 10% of the LBA range, you should have 90% of the LBA range in addition to the normal reserve. This should mean that = you=E2=80=99ve got 10x the normal reserve (since normally the reserve is in the 10% = range, give or take). SD cards don=E2=80=99t lose capacity. Then tend to fail = read-only or read-never when they reach their end of life. So let=E2=80=99s do the math. 512MB cards tended to have write speeds of = maybe 6MB/s. At 6MB/s, that=E2=80=99s about 518MB/day, or one drive write per day. = Most SD cards, when you can find a rating, are good for between 0.3 and 1 drive write = per day over their life (some are more durable, granted). 0.3 DWPD would mean = that we=E2=80=99re putting wear not he part at 3x the normal rate. Over several month, = that=E2=80=99s nowhere near the 3 year design point that most SD cards implement. It=E2=80=99s = maybe 2 years of wear tops. If it=E2=80=99s a better card, it isn=E2=80=99t even one year = worth of writes. So it isn=E2=80=99t too surprising that Ian=E2=80=99s experience = wasn=E2=80=99t so horrible. I ran a similar experiments and failed to wear things out. It wasn=E2=80=99t until I = worked at a NAND card maker that I ever wore out NAND. And to do that I had to wear out = some tiny percentage of the drive by artificially limiting the range of NAND = used to a range of erase blocks (usually around 50 or maybe 10 GB of space) and = writing at full speed (something in the neighborhood of 1GB/s) would give maybe 50 P/E cycles an hour (due to swell limitations), leading to wear out = over a long weekend=E2=80=A6 And that=E2=80=99s using ~1% of the capacity of the = drive at a time. Warner --Apple-Mail=_8C9DC301-4A05-4F2E-A703-6D525CB13CFC Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJW8MBcAAoJEGwc0Sh9sBEAJWkP/R/Jf+tROSgcTlhhJC2Z4S5W zi0knjml1KFchPzEpxkAwvmmBVrNLewbDgAYYO9UZtzw4b+wAtLBG/Hj/AB1V/tR RcCtvsm8ovTjpJQxzDEZ7UvGW1oecjMwjYHkrW11JbkGmuMsrH03KyxYv+E7YLc/ hdEFjNA9+jFy52lTIsu2r37/CXshyzt1BLIJS1enyGXq7ByV1e7XJ/E23AaXXoNe 3y4FRqddZIHE9vK8wp2HPEksCk9BGqtaqThtSWB0VuOK0gsxiP+kgS+ARrwHBv90 KjZReSTtScQlDFg0jNj2V2LV/cjL6QGITSUsO3fAiPHrfkQErrfdNVx91WHAF1EK lKRa59MGyxcA4zYPtvJ3be+z7O6DCVDZ8e4dYgkqPDPma3YucotSzHaX+XczomAa 76WiBB4oRRifmlqMjdSjKd+NCNQx3z/dyzjSlwISv9JHHcX14SMNFDX2OlWCd9WH dJvO8qXlGWC3bFBYjfISlvNKuTKLkl3CktKPQDb4PVknZG3VVzTLrJa4gXoizkQo vAcAEBcYjY3DUdAA5nkfdVe4nJV0tJUiEiwt7iRAisy5wuCwhDh4/TXSVebwFss0 c605dUMFHXNciCzGG9mBf0wTR7QFDgWwzkxCA3cgJHVy32epHRmacNW/iLXrjLDm XTEfRIa8Fs3pS0vPoYCc =k5q9 -----END PGP SIGNATURE----- --Apple-Mail=_8C9DC301-4A05-4F2E-A703-6D525CB13CFC--
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?E985EBE6-E062-4C5E-8F85-ECB7BDE98DE8>