Date: Mon, 21 Mar 2016 13:01:24 -0600 From: Ian Lepore <ian@freebsd.org> To: bob prohaska <fbsd@www.zefox.net>, freebsd-arm@freebsd.org Subject: Re: Effect of partitioning on wear-leveling Message-ID: <1458586884.68920.96.camel@freebsd.org> In-Reply-To: <20160321175952.GA83908@www.zefox.net> References: <20160321175952.GA83908@www.zefox.net>
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On Mon, 2016-03-21 at 10:59 -0700, bob prohaska wrote: > To the extent that FreeBSD on ARM uses wear leveling on flash > devices, > does the partition layout have any effect on how or if wear leveling > works? > > The puzzle at hand is an RPI2 with /boot/msdos and / on the microSD > card > and /usr on USB flash. /var and /tmp will be on microSD, but it's not > clear > whether they should be in the / partition or isolated. > > Thanks for reading, and any guidance! > 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
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