Cody Dunne wrote:
> 
>>     * Pool is 587.09GB comprising 31187909 files and 4369 directories
>>       (as of 2009-03-11 14:46),
> 
> Has anyone else noticed that all the posted pool information has 4369 
> directories listed for the pool? Mine does as well.

There's a tree structure designed to limit the number of entries in any 
single directory, and that is just the top level.  Unix file systems are 
notoriously bad at scaling the number of directory entries up. When you 
want to create a new file, the OS has to scan the whole existing 
directory to see if the name exists, then insert it, keeping it locked 
the whole time to avoid races with other processes that might be 
inserting the same name (with obvious tradeoffs for the ones that build 
  an index for the names vs. doing a linear scan)  So, for example, 
hashed name fff86d95a3314b50e891c345014053ec lands under cpool/f/f/f.

I don't know if anyone has tried fewer or more levels to see how 
performance is affected.  Squid uses 2 levels of 2 character directory 
names 00-FF for the same purpose for comparison.

-- 
  Les Mikesell
    lesmikesell AT gmail DOT com


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