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>
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[-- Attachment #1 --] > On Mar 21, 2016, at 9:28 PM, bob prohaska <fbsd@www.zefox.net> wrote: > > On Mon, Mar 21, 2016 at 04:41:10PM -0600, Ian Lepore wrote: >> >> 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). >> >> > 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’ve got 10x the normal reserve (since normally the reserve is in the 10% range, give or take). SD cards don’t lose capacity. Then tend to fail read-only or read-never when they reach their end of life. So let’s do the math. 512MB cards tended to have write speeds of maybe 6MB/s. At 6MB/s, that’s 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’re putting wear not he part at 3x the normal rate. Over several month, that’s nowhere near the 3 year design point that most SD cards implement. It’s maybe 2 years of wear tops. If it’s a better card, it isn’t even one year worth of writes. So it isn’t too surprising that Ian’s experience wasn’t so horrible. I ran a similar experiments and failed to wear things out. It wasn’t 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… And that’s using ~1% of the capacity of the drive at a time. Warner [-- Attachment #2 --] -----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-----
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