UFS2 limits

Matthew Seaman m.seaman at infracaninophile.co.uk
Sun Nov 9 04:16:34 PST 2008

Jeremy Chadwick wrote:

> I don't want to change the topic of discussion, but I *highly* recommend
> you ***stop*** whatever it is you're doing that is creating such a
> directory structure.  Software which has to iterate through that
> directory using opendir() and readdir() will get slower and slower as
> time goes on.

With the implementation of UFS_DIRHASH the practical limit on the
size of directories is now a great deal larger. In particular
the slow down caused by linear search through the contents has been 
eliminated.  See ffs(7).  10,000 files or sub-directories, whist
not a particularly elegant setup, is actually not unworkable

As for the maximum number of subdirectories it is possible to create
on UFS2 -- it is limited by the inode structure to a 16 bit quantity.

% jot 100000 1 | xargs mkdir -v
3273mkdir: 32766: Too many links
mkdir: 32767: Too many links
mkdir: 32768: Too many links
mkdir: 32769: Too many links
mkdir: 32770: Too many links
mkdir: 32771: Too many links

Which is 32768 - 2 for the '.' and '..' links.  Trying to create too
many subdirectories just results in mkdir failing: the filesystem
itself is not damaged.



Dr Matthew J Seaman MA, D.Phil.                   7 Priory Courtyard
                                                  Flat 3
PGP: http://www.infracaninophile.co.uk/pgpkey     Ramsgate
                                                  Kent, CT11 9PW

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