Date: Tue, 22 Mar 2016 14:14:32 +0800 From: Erich Dollansky <erich@alogt.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: <20160322141432.3f0a3a61@X220.alogt.com> In-Reply-To: <20160321221153.GB83908@www.zefox.net> References: <20160321175952.GA83908@www.zefox.net> <1458586884.68920.96.camel@freebsd.org> <20160321221153.GB83908@www.zefox.net>
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Hi, On Mon, 21 Mar 2016 15:11:53 -0700 bob prohaska <fbsd@www.zefox.net> wrote: > On Mon, Mar 21, 2016 at 01:01:24PM -0600, Ian Lepore wrote: > > > > Freebsd does no wear-leveling, it's up to the microcontrollers > > within the storage devices to do that. > > > > Those controllers have no notion of partitioning or filesystem > > layout and do whatever they want to do internally about wear > > leveling. That leads to the mildly disturbing situation of having > > blocks from a readonly filesystem and blocks from a writable > > filesystem sharing the same flash erase-block inside the device. > > One likes to think of the data in a readonly filesystem as safely > > protected from the read-modify -write activity that happens at the > > flash erase-block level, but no such g'tee is made on any mmc, sd, > > or usb flash-based devices I know of. > > > > - Ian > > > Ok, thanks. It sounds like /var and /tmp could be confined to > limited-size partitions while still permitting wear leveling to use > other, less-used parts of the device. So, if a block nominally > in /var reaches end of life can the wear leveling controller start > stashing data anywhere on the device? > > As a practical matter, should I even be worrying about this? Folks > once made a big deal of partitioning storage so a runaway process > couldn't choke the whole machine. Is the precaution still worth > taking on ARM? > we use memory disk for /var and /tmp. If you really need the content of these directories, you could write them back to flash by a script every hour or so and save all the writes between. Do not forget the flash devices used in Raspberries & Co. cannot be compared with the flash devices used in flash disk. Erich
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