Date: Wed, 20 Sep 2006 02:01:23 +0930 From: Wayne Sierke <ws@au.dyndns.ws> To: freebsd-questions@freebsd.org Subject: Reducing reserved space on large filesystems Message-ID: <1158683484.851.166.camel@ovirt.dyndns.ws>
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I was very interested to read the following written by Matthew Seaman in 2004. http://lists.freebsd.org/pipermail/freebsd-questions/2004-January/033754.html The parameters given to newfs(8) don't depend on the size of the filesystem, so much as the size of the files you intend to store within it, and the sort of directory structure you want to use (ie. how many files per directory) Many of the tunables in newfs(8) to do with the details of disk geometry don't make sense with modern drives and should be ignored. You should try running 'newfs -N' with various values for the '-g' average file size and '-h' average numbers of files per directory parameters to see what sort of numbers it spits out. You don't have to be too accurate with those file size and files per directory estimates -- order of magnitude is generally good enough. Unless you're going to be storing exceptionally large files (say, typical size 20Mb) or you want to have directories with 5,000 or more files in them, then just using the newfs(8) default values will work very well. One thing you can do for any file system over about 256Mb is drop the free space reserve ('-m' option in newfs(8), or it can be modified in an existing filesystem using tunefs(8)). 1% is more than adequate if you're creating a multi-gigabyte filesystem. I'm especially interested in the comment about the 'free space reserve' which flies in the face of everything I can recall ever reading that has always mirrored the warnings in tuning(7) and tunefs(8) about the perils of reducing the reserved space below the default. However I didn't see any reply to Matthew's email to repudiate his statements. What are people's experiences in the field? Are the cautions now much less relevant with modern hard-drive capacities and performance?
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