Date: Sat, 10 Feb 2007 01:12:07 -0600 From: Eric Anderson <anderson@freebsd.org> To: Antony Mawer <fbsd-fs@mawer.org> Cc: freebsd-fs@freebsd.org, Ivan Voras <ivoras@fer.hr> Subject: Re: comments on newfs raw disk ? Safe ? (7 terabyte array) Message-ID: <45CD7047.3040901@freebsd.org> In-Reply-To: <45CD0C5A.3070804@mawer.org> References: <646424.65334.qm@web58613.mail.re3.yahoo.com> <eqhrv8$92j$1@sea.gmane.org> <45CC793F.7090003@freebsd.org> <45CD0C5A.3070804@mawer.org>
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On 02/09/07 18:05, Antony Mawer wrote: > On 9/02/2007 3:38 AM, Eric Anderson wrote: >>> Only "collateral" problems because of the partition size: a regular >>> (non-softupdates) fsck will take a LONG time to finish and eat a LOT of >>> memory while it's doing its stuff. You'll need a lot of swap space (1GB >>> per TB? someone had empirical numbers on this, I'm sure) if you think >>> you'll need to fsck it entirely. Creating snapshots will also take a >>> long time on it, and you probably want to search the lists for >>> recommendations about creating snapshots in a second level directory in >>> order not to block the root directory. Related to this is >>> background-fsck which works by creating snapshots, so you'll probably >>> want to disable it. >> I have 5 10Tb file systems (and some 2Tb ones, but who cares about those >> tiny things? :)), and I can tell you that an empty huge file system is >> pretty easily fsck-able, but a full one will kill you. It greatly >> depends on how many files (inodes) you have used on the file system. If >> you have a massive amount of small files, you'll be eating up a ton of >> memory. My 'rule of thumb' for my data (which averages to about >> 16k/file) is 1G of memory for each 1Tb of disk space used. So, on a >> 10Tb file system, if I ever want the fsck to complete, I need an AMD64 >> box with *at least* 10G of memory, plus a lot of time. A *lot* of time. >> By 'a lot', I mean anywhere from a day, to several days. > > Has anyone looked at the changes in DragonFly that were made in the 1.8 > release? I noticed the other day, reading the release notes > (http://www.dragonflybsd.org/community/release1_8.shtml) the point: > > "Greatly reduce the memory allocated by fsck when fscking filesytems > with a huge number of directories (primarily mirors with lots of > hardlinked files). Otherwise fsck can run out of memory on such > filesystems." > > Whether or not this helps in the general case, or only the scenario > described, I do not know... but it would be interesting for someone with > enough filesystem-foo to have a look at! > > --Antony I'll check that out - didn't know about it, thanks! Eric
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