How many files can I put in a directory?

Question

Does it matter how many files I keep in a single directory? If so, how many files in a directory is too many, and what are the impacts of having too many files? (This is on

Answer 1

ext3 does in fact have directory size limits, and they depend on the block size of the filesystem. There isn't a per-directory "max number" of files, but a per-directory "max number of blocks used to store file entries". Specifically, the size of the directory itself can't grow beyond a b-tree of height 3, and the fanout of the tree depends on the block size. See this link for some details.

https://www.mail-archive.com/cwelug@googlegroups.com/msg01944.html

I was bitten by this recently on a filesystem formatted with 2K blocks, which was inexplicably getting directory-full kernel messages warning: ext3_dx_add_entry: Directory index full! when I was copying from another ext3 filesystem. In my case, a directory with a mere 480,000 files was unable to be copied to the destination.