What's the maxium number of files a Unix folder can hold?

Question

What's the maxium number of files a Unix folder can hold?

I think it will be the same as the number of files.

Answer 1

Varies per file system, http://en.wikipedia.org/wiki/Comparison_of_file_systems

Answer 2

On all current Unix filesystems a directory can hold a practically unlimited number of files. Whereas "unlimited" is limited by diskspace and inodes - whatever runs out first.

With older file system designs (ext2, UFS, HFS+) things tend to get slow if you have many files in a directory. Usually things start getting painful around 10,000 files. With newer filesystems (ReiserFS, XFS, ZFS, UFS2) you can have millions of files in a directory without seeing general performance bottlenecks.

But having so many files in a directory is not well tested and there are lots of tools which fail that. For example, periodic system maintenance scripts may barf on it.

I happily used a directory with several million files on UFS2 and had seen no problems until I wanted to delete the directory - that took several DAYS.

Answer 3

I assume you are thinking of storing a lot of files in one place, no?

Most modern Unix files systems can put a lot of files in one directory, but operations like following paths, listing files, etc. involve a linear search through the list of files and get slow if the list grows too large.

I seem to recall hearing that a couple of thousand is too many for most practical uses. The typically solution is to break the grouping up. That is,

/some/path/to/dir/a/
/some/path/to/dir/b/
...
/some/path/to/dir/z/

and store your files in the appropriate sub-directory according to a hash of their basename. Choose a convenient hash, the first character might do for simple cases.

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Cristian Ciupitu writes in the comments that XFS, and possibly other very new file-systems, use log(N) searchable structures to hold directory contents, so this constraint is greatly ameliorated.

Answer 4

It depends how many inodes the filesystem was created with. Executing

df -i 

will give you the number of free inodes. This is the practical limit of how many files a filesystem and hence a directory can hold.

Answer 5

ext3 one of the most common linux filesystem formats gets really sluggish if you have around 20k + file in a directory. Regardless of how many it can hold, you should try to avoid having that many files in one directory.

Answer 6

From the comment you left, I think you don't really care about how many files/folders your FS can host.

You should probably consider using ModRewrite and rewriting site.com/username to site.com/?user= or something of the kind and store all your data in a database. Creating one folder per user is generally not necessary (and not a good idea).

That said, each filesystem has limits, and df can tell you how many inodes are available on each partition of your system.