Jim, The wear leveling algorithms have gotten very good at garbage collection, wear leveling, and bit error recovery codes. (LDPC has gotten a lot of practical research for flash). (the challenges are - when to do the garage collection, so as not to impact read and write rates, yet not run so low that write IOP rate falls off a cliff, AND still keep pages alive).
File systems that try to understand the flash sectors generally haven’t proven as helpful as the flash device controller wear leveling algorithms. A lot of the SD cards have gone to TLC style memory (also know as trash). KR > On Dec 8, 2021, at 2:35 PM, Lux, Jim <j...@luxfamily.com> wrote: > > On 12/8/21 2:15 PM, Bill Dailey wrote: >> You can also set them up so they don’t write to the SD once everything is >> set. SD’s will last forever like this. Basically read only and RAM disk. > > > yes indeed - these days, with lots o'RAM on a rPi, you should boot off the SD > (or eMMC) and run out of RAM. For a "clock" application, you could probably > structure your writes to SD (for nonvolatile storage of logs, etc.) so that > you limit the number of writes. If you log once an hour that's just under > 9000 writes/year. > > Typical MLC flash is good for at least 10,000 erase cycles on a page. Writing > data to an erased page (or the part that's not already written) doesn't wear > it out, but changing data in the middle of a file does, because you have to > erase it (consuming life), and then rewrite. > > There are Journaling File Systems that deal with this, but I doubt they're > compatible with the wear leveling systems in commercial SD cards. Basically, > the SD card has a controller that exposes a generalized interface, with the > wear leveling hidden from you, and if it's hidden, then the JFS doesn't > really know how to manage the device. > > I don't know, though, it's a fertile ground - and someone may have a nice JFS > for a common distro for RPi and SD card. > > > If you want to get real down and dirty, there are also clever schemes that > write all ones or zeros (depending on the device), instead of erasing, and > then the reader of the file knows that this means "not used" - Much like the > RUBOUT character on paper tape, or a similar scheme used with PROMS where you > don't want to erase it. > > _______________________________________________ > time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an > email to time-nuts-le...@lists.febo.com > To unsubscribe, go to and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com -- To unsubscribe send an email to time-nuts-le...@lists.febo.com To unsubscribe, go to and follow the instructions there.
