Date: Wed, 23 Mar 2016 00:32:30 -0600 From: Warner Losh <imp@bsdimp.com> To: Russell Haley <russ.haley@gmail.com> Cc: bob prohaska <fbsd@www.zefox.net>, freebsd-arm <freebsd-arm@freebsd.org> Subject: Re: Effect of partitioning on wear-leveling Message-ID: <CANCZdfpbxwkt%2BAujZBzGTStbweX=paPJ3SLD_cBf4KyA8m5ADA@mail.gmail.com> In-Reply-To: <CABx9NuSfUfQudmUESX-MbA7-oL3R0s1LvvPeg-_gWVjfTAPtaw@mail.gmail.com> References: <20160321175952.GA83908@www.zefox.net> <1458586884.68920.96.camel@freebsd.org> <20160321221153.GB83908@www.zefox.net> <1458600070.68920.107.camel@freebsd.org> <1973487B-0AA7-468D-A9CC-319FBE2122F0@netgate.com> <CANCZdfrCWXAswe02Qd3tTiDL8O_4TGEWbhFqgft4Q9aKj7ixvg@mail.gmail.com> <20160322033417.GD83908@www.zefox.net> <271EF73A-077C-44A5-8B58-721405800B9F@bsdimp.com> <CABx9NuSfUfQudmUESX-MbA7-oL3R0s1LvvPeg-_gWVjfTAPtaw@mail.gmail.com>
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On Mon, Mar 21, 2016 at 10:39 PM, Russell Haley <russ.haley@gmail.com> wrote: > How long can nand go without power before it starts to lose data integrity? > It depends on the NAND. Most NAND is spec'd for 1 of 3 common values: 1 month, 3 months or 1 year. This spec is the 'end of life' spec, and always at 40C. When the NAND is worn out, it will still be readable after it has been off for this period of time. Temperature does have a lot to do with it. At 0C, NAND can last up to 80 times longer, in theory. Likewise, at 70C, it will age 80 times faster. It's generally an Arrhenius relationship between temperature and data retention. The hotter the nand, the less long data lasts, though the faster the program and erase times (and the greater damage each P/E cycle causes). The colder the nand, the longer the retention, but the slower the program and erase times are. NAND chips, by themselves, generally don't care power on or not. Devices they are put in care a great deal. Part of the garbage collection that's done by NAND devices ensures that the data is never put at undue risk. That's done by copying the active data out of blocks that are too old, or too hard to read. The details vary FTL to FTL, some will scan the device once in a while to make sure data can still be written, others do it mechanically with the passage of time. Data can be too hard to read if it is too old, or if it has been read too many times... Warner
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