- EXT3 supports 32,000 subdirectories.
- EXT4 supports 64,000...
- I've read about people having millions of subdirectories on the XFS filesystem, but can't find an exact value referenced anywhere.
How many subdirectories does the XFS filesystem support?
There are of course other practical considerations....like the total length of a filename allowed which may be far less than the number of subdirectories allowed.
Anyway, a subdirectory is just a file anyway, so isn't the absolute maximum number of subdirectories is theoretically the max number of i-nodes on a specific filesystem?
I do not think there is a hard limit except for the maximum file size of 2^64-1 bytes. But there would be a couple of "soft" limits - searching a large directory might become inefficient due to high CPU and/or memory intensity.
From the XFS project site at SGI (a bit aged already):