[Gluster-users] Adding new volumes to DHT

Moritz Krinke mkrinke at fotocommunity.net
Wed Jul 22 12:25:44 UTC 2009


i just did a test about that.
if you add another subvolume to the DHT volume and add new files into  
an existing directory they will be distributed over all DHT-subvolumes.

I assume that the distribution on old subvolumes will stop when the  
free-space threshold is reached, but i did not test that.


Am 21.07.2009 um 18:57 schrieb Barry Jaspan:

> I have a question about this paragraph from the "Understanding DHT  
> Translator":
> "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.
> Thanks,
> Barry
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