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List:       freebsd-hackers
Subject:    RE: format/newfs larger external consumer drives
From:       Andrew Duane <aduane () juniper ! net>
Date:       2015-07-24 12:34:00
Message-ID: DM2PR05MB736A3B6ED705DE07BDB322DCE810 () DM2PR05MB736 ! namprd05 ! prod ! outlook ! com
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> -----Original Message-----
> From: owner-freebsd-hackers@freebsd.org [mailto:owner-freebsd-
> hackers@freebsd.org] On Behalf Of Don whY
> Sent: Thursday, July 23, 2015 8:52 PM
> To: freebsd-hackers@freebsd.org
> Subject: Re: format/newfs larger external consumer drives
> 
> On 7/22/2015 2:08 PM, Dieter BSD wrote:
> > Don whY asks:
> > > So, fsck's effort (and execution *time*) is based *mostly* on inodes?
> > 
> > I don't know about *mostly*, but reducing the number of inodes
> > significantly reduced fsck time for me.
> 
> OK.  I may try building a filesystem, loading a fixed set of files
> (assorted) onto it, then fsck'ing it.  Then, rebuild with a different
> block/frag/inode configuration and try again (same file set).  At the very least, \
> it will be an interesting experiment!

FSCK has 5 passes, each of which checks a different "thing" in the filesystem. Each \
pass will depend on how many of those "things" there are to check. One checks inodes \
and cylinder groups, one checks all blocks, one checks all directory and file \
entries, and so on. So fewer inodes will help, but more files eat up the savings, \
etc. Some experiments can tell you how long it takes to check each and what the \
savings would be.

Also remember that each inode takes 128 bytes on disk. So a billion unused inodes \
wastes a 128 GB on the disk.

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