[Gluster-users] Adding new volumes to DHT

Barry Jaspan barry.jaspan at acquia.com
Tue Jul 21 16:57:52 UTC 2009

I have a question about this paragraph from the "Understanding DHT  

"Currently hash works based on directory level distribution. i.e, a  
given file's parent directory will have information of how the hash  
numbers are mapped to subvolumes. So, adding new node doesn't disturb  
any current setup as the files/dirs present already have its  
information preserved. Whatever new directory gets created, will start  
considering new volume for scheduling files."

The last sentence suggests that if I have a single directory on a DHT  
volume and it is getting full, adding additional subvolumes to the DHT  
volume will not help because all the files in a directory will only  
ever live in subvolumes that existed at the time the directory is  
created.  Is that true?

Also, it sounds like an entry mapping each filename (hash number) to a  
subvolume is stored in the extended attributes of the parent directory  
for that file.  What is the practical limit for the number of files  
that can be stored in a single directory under this system?  It seems  
like eventually doing a lookup in the directory's attributes would  
itself become a very expensive operation.


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