Date: Wed, 2 Jul 2014 09:32:52 +0100 (BST) From: Anton Shterenlikht <mexas@bris.ac.uk> To: imp@bsdimp.com, mexas@bris.ac.uk Cc: freebsd-arm@freebsd.org Subject: Re: /tmp, /var/log, /var/tmp as /dev/md - why? Message-ID: <201407020832.s628WqWE014903@mech-cluster241.men.bris.ac.uk> In-Reply-To: <C8EFA73F-5D47-45A3-AF58-65E59A0BED95@bsdimp.com>
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>From imp@bsdimp.com Tue Jul 1 18:09:59 2014 > >On Jul 1, 2014, at 3:25 AM, Anton Shterenlikht <mexas@bris.ac.uk> wrote: > >> Why is it a good idea to mount /tmp and some var dirs on memory disks: >>=20 >> root@raspberry-pi:/usr/ports # df -m >> Filesystem 1M-blocks Used Avail Capacity Mounted on >> /dev/mmcsd0s2a 14694 777 12742 6% / >> devfs 0 0 0 100% /dev >> /dev/mmcsd0s1 16 3 13 20% /boot/msdos >> /dev/md0 28 4 22 16% /tmp >> /dev/md1 14 0 12 0% /var/log >> /dev/md2 4 0 4 0% /var/tmp >> root@raspberry-pi:/usr/ports #=20 >>=20 >> Is this about speed or power, or maybe space? >>=20 >> Can I not put all these dirs on sd card? >>=20 >> I'm new to arm, so maybe things are different >> to other arches. > >It isn=92t so much about ARM as it is about SD cards. Each write to a = >file causes wear and tear on the card. Each update of metadata likewise. = >There are things that can be done (like enabling trim) that reduce the = >wear and tear on the card, NAND flash only has so much life. Do you = >really want to use it for data that=92s at best disposable? No. SD cards = >these days are made from NAND that=92s lucky to get 3k separate writes = >to it (or even worse: 500 in the case of TLC NAND). Given such a limited = >resource, nanobsd, and others, use MD devices to eliminate that wear and = >tear. It is the same rason there=92s no swap partition... > >Having said that, I=92ve run many development systems without doing = >this. They work fine, but doing it in production has shown to result in = >some SD cards (not all) breaking prematurely. > >Warner Wow, thank you! I knew nothing about sd cards, so this is very helpful. So, if I need to build kernel, world and ports often, sd card is a poor choice? I better use an external disk? What I really want to find out is whether I can have a dumb graphical terminal from Rpi-B. Thanks Anton
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