Date: Tue, 1 Jul 2014 09:35:29 -0600 From: Warner Losh <imp@bsdimp.com> To: mexas@bris.ac.uk Cc: freebsd-arm@freebsd.org Subject: Re: /tmp, /var/log, /var/tmp as /dev/md - why? Message-ID: <C8EFA73F-5D47-45A3-AF58-65E59A0BED95@bsdimp.com> In-Reply-To: <201407010925.s619PHeT006679@mech-cluster241.men.bris.ac.uk> References: <201407010925.s619PHeT006679@mech-cluster241.men.bris.ac.uk>
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--Apple-Mail=_6751D0A8-49EB-4125-B282-7935AE8F50C0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=windows-1252 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 --Apple-Mail=_6751D0A8-49EB-4125-B282-7935AE8F50C0 Content-Transfer-Encoding: 7bit Content-Disposition: attachment; filename=signature.asc Content-Type: application/pgp-signature; name=signature.asc Content-Description: Message signed with OpenPGP using GPGMail -----BEGIN PGP SIGNATURE----- Comment: GPGTools - https://gpgtools.org iQIcBAEBCgAGBQJTstVCAAoJEGwc0Sh9sBEA1fAP/05hPbwe8Nh03ZKbUoJTSIJV P23q8KXX0ocRKwT8AJedhpNqTWHFTkAzF0cIGLEiatxQnsRSAosVDisAxZNlqYxH uA417z6EWt68R9BnTBCFu5/UmagszH1i6KSWTXWmxR2e8ltGSqf4RgXRj9qzJKKo UhNOsHsoI29820kErS7oykCMBSL+EinVOs/HI6OGm4Lnnu3crUHTMdces+TMXTk9 oG4R7KLPWNDJTXBdPrNyJysVnrM94/GvG+/6C1qG8T2b30oLdOS8jj7OU3mtkYJv QHBsiz011LxZAsLXpCQcTZj0xb/SzJ1jdI3p8XlBAVNNsWtxcpARV+3HuO1fBfOJ Psxyv0urhIAOsRqSZ63bg/MWP0U+3p3nGCV/0z5xmZV6iiXpexertFj+1/WOyvU2 nxxmbvpNtplQLI5jJCSCdBhKVqO2risEOxetSgMFCHLUTPMZ2eMsIVWATPSO0fiI M1XqR7eKaLcpnJZZtk9Gc6zet1CfiwxeLQzR8Thd56pgQpt7k0+Lul99Lxq9qe4K GumOGLF3SOV+282K/XJMCu5eNl+90HA51X6HZ+Gkj9PSI+rFGNcqOyOmmbn8RHWV yOpaX43fqX75GtjYIBWhRE/wJpUa7V3wgHDjGBQYv1RwzwlLO+eaeRI0efvT3lfW hM/LVl5NvOVtZ5J3behQ =yh03 -----END PGP SIGNATURE----- --Apple-Mail=_6751D0A8-49EB-4125-B282-7935AE8F50C0--
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