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Chapter 32. Handling Large Directories

Jeremy Allison

Samba Team

John H. Terpstra

Samba Team

March 5, 2005

Samba-3.0.12 implements a solution for sites that have experienced performance degradation do to the problem of using Samba-3 with applications that need large numbers of files (100,000 or more) per directory.

The key was fixing the directory handling to read only the current list requested instead of the old (up to samba-3.0.11) behaviour of reading the entire directory into memory before doling out names. Normally this would have broken OS/2 applications which have very strange delete semantics, but by stealing logic from Samba4 (thanks tridge) the current code in 3.0.12 handles this correctly.

To set up an application that needs large number of files per directory in a way that does not damage performance unduly follow these steps:

Firstly, you need to canonicalize all the files in the directory to have one case, upper or lower - take your pick (I chose upper as all my files were already upper case names). Then set up a new custom share for the application as follows:

[bigshare]
        path = /home/jeremy/tmp/manyfilesdir
        read only = no
        case sensitive = True
        default case = upper
        preserve case = no
        short preserve case = no

Of course, use your own path and settings, but set the case options to match the case of all the files in your directory. The path should point at the large directory needed for the application - any new files created in there and in any paths under it will be forced by smbd into upper case - but smbd will no longer have to scan the directory for names - it knows that if a file does not exist in upper case then it doesn't exist at all.

The secret to this is really in the case sensitive = True line. This tells smbd never to scan for case-insensitive versions of names. So if an application asks for a file called FOO, and it can not be found by a simple stat call, then smbd will return file not found immediately without scanning the containing directory for a version of a different case. The other xxx case xxx lines make this work by forcing a consistent case on all files created by smbd.

Remember, all files and directories under the path directory must be in upper case with this smb.conf stanza as smbd will not be able to find lower case filenames with these settings. Also note this is done on a per-share basis, allowing this to be set only for a share servicing an application with this problematic behaviour (using large numbers of entries in a directory) - the rest of your smbd shares don't need to be affected.

This makes smbd much faster when dealing with large directories. My test case has over 100,000 files and smbd now deals with this very efficiently.