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According to says:

Right now the maximum possible number of sub directories contained in a single directory in Ext3 is 32000. Ext4 breaks that limit and allows unlimited number of sub directories.

But the Wikipedia says:

In ext3 the number of subdirectories that a directory can contain is limited to 32,000. This limit has been raised to 64,000 in ext4, and with the "dir_nlink" feature it can go beyond this (although it will stop increasing the link count on the parent).

So to go beyond 64k do I need dir_nlink? I am specifically interested in Ubuntu 9.10 if that makes a difference.

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up vote 1 down vote accepted

Well, both is correct, Wikipedia is just a bit more detailed. So in short

  • yes, ext4 allows an unlimited number of sub directories
  • yes, to use more than 32,000 subdirs, you need the dir_nlink feature

The reason the Ext4 HOWTO does not mention this is that apparently dir_nlink is handled transparently. It is just a feature of the ext4 driver in the Linux kernel, so you only need to worry that your Linux kernel is recent enough.

The patch was apparently submitted in July 2007

so it'r probably in Linux 2.6.22 at the latest. So any recent distro will have it; I guess that's why the Ext4 HOWTO does not mention it.

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